JP7549611B2 - Apparatus, system, method, and computer readable medium for enhancing cellular systems to support multi-SIM user equipment - Patents.com - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Patent Application No. 62/928,379, filed October 31, 2019, U.S. Provisional Patent Application No. 62/899,322, filed September 12, 2019, and U.S. Provisional Patent Application No. 62/858,747, filed June 7, 2019, the entire contents of which are incorporated herein by reference.

The present disclosure relates generally to wireless communications, and more particularly to wireless communications systems, devices, methods, and computer-readable media with computer-executable instructions for enhancing cellular systems to support the use of 4G and 5G multi-subscriber identity module (SIM) user equipment (UE).

The "Background Art" discussion provided herein is intended to generally present the context of the present disclosure. To the extent that it is described in this Background Art section, the inventors' work, as well as aspects of the description that may not have qualified as prior art at the time of filing, are not expressly or impliedly admitted as prior art to the present invention.

To date, multiple SIM UEs are proprietary solutions implemented by device manufacturers without knowledge of the core network and are outside the scope of 3GPP standards. The behavior of the cellular network was designed where the behavior of the various entities (UE, RAN, and CN) is well defined and known between the various entities. With the various implementations of existing multiple SIM UEs, the various behaviors of the various implementations can negatively affect the operation of the network and even degrade its performance.

An exemplary embodiment of the present disclosure provides an electronic device including a receiver configured to receive a first subscriber identity module (SIM), a receiver configured to receive a second SIM, and circuitry configured to receive data from the first SIM and send a request to a first public land mobile network (PLMN) to register the electronic device with the first PLMN, the request indicating that the electronic device is a multi-SIM device, the request including multi-SIM support information, the multi-SIM support information informing the first PLMN of a preference of the electronic device for multi-SIM operation.

An exemplary embodiment of the present disclosure provides a method performed by an electronic device, the method including steps of receiving data from a first subscriber identity module (SIM) and sending a request to a first public land mobile network (PLMN) to register the electronic device with the first PLMN, the request indicating that the electronic device is a multi-SIM device, the request including multi-SIM support information, the multi-SIM support information informing the first PLMN of the device's preferences for multi-SIM operation.

An exemplary embodiment of the present disclosure provides a non-transitory computer-readable medium including computer-executable instructions that, when executed by an electronic device, cause the electronic device to receive data from a first subscriber identity module (SIM) and send a request to a first public land mobile network (PLMN) to register the electronic device with the first PLMN, the request indicating that the electronic device is a multi-SIM device, the request including multi-SIM support information, and the multi-SIM support information informing the first PLMN of the device's preferences for multi-SIM operation.

This Summary is provided to introduce in a simplified form a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Moreover, the claimed subject matter is not limited to limitations that solve any or all of the disadvantages noted in any part of this disclosure.

The scope of the present disclosure is best understood from the following detailed description of exemplary embodiments when read in conjunction with the accompanying drawings.

FIG. 1A is a system diagram illustrating an example 3GPP architecture. FIG. 1B is a system diagram illustrating an example of a radio access network (RAN) architecture and a core network architecture. FIG. 1C is a system diagram illustrating an example of a radio access network (RAN) architecture and a core network architecture. FIG. 1D is a system diagram illustrating an example of a radio access network (RAN) architecture and a core network architecture. FIG. 1E is a system diagram illustrating an example 3GPP architecture. FIG. 1F is a system diagram of an exemplary apparatus or device configured for wireless communication. FIG. 1G is a system diagram illustrating an example of a computing system for use in a communications network. FIG. 2 is a diagram illustrating a non-roaming 5G system architecture according to an example embodiment. FIG. 3 is a diagram illustrating a roaming 5G system architecture according to an example embodiment. FIG. 4 is a diagram illustrating a roaming 5G system architecture according to an example embodiment. FIG. 5 illustrates a 5G general registration procedure according to an example embodiment. FIG. 6 illustrates a registration management state model in a UE according to an example embodiment. FIG. 7 is a diagram illustrating connection management state transitions in a UE according to an example embodiment. FIG. 8 illustrates a network slice-specific authentication and authorization method according to an exemplary embodiment. FIG. 9 illustrates a method for UE registration with multiple SIMs according to an example embodiment. FIG. 10 illustrates a method for partial registration according to an example embodiment. FIG. 11 illustrates an alternative method of partial registration according to an example embodiment. FIG. 12 illustrates a method for indirect registration according to an example embodiment. FIG. 13 illustrates an alternative method of indirect registration according to an example embodiment. FIG. 14 is a diagram illustrating an RM-INACTIVE registration management state according to an example embodiment. FIG. 15 illustrates a paging method for multi-SIM operation according to one example embodiment. FIG. 16 illustrates a SIM switching method according to an example embodiment. FIG. 17 illustrates a multi-SIM configuration GUI according to an example embodiment. FIG. 18 illustrates an individual SIM configuration GUI according to an example embodiment. FIG. 19 is a diagram illustrating a 3GPP EPS non-roaming system architecture according to an example embodiment. FIG. 20 illustrates an EPS attach procedure according to an exemplary embodiment. FIG. 21 is a diagram illustrating EPS Mobility Management (EMM) states according to an example embodiment. FIG. 22 is a diagram illustrating EPS connection management states according to an example embodiment. FIG. 23 illustrates a service request procedure triggered by an EPS network according to an exemplary embodiment. FIG. 24 illustrates a method of partial attachment according to one exemplary embodiment. FIG. 25 illustrates a method of indirect attachment according to one exemplary embodiment. FIG. 26 illustrates a method for multiple SIM attachment according to an example embodiment. FIG. 27 is a diagram illustrating the EMM-INACTIVE state according to one example embodiment. FIG. 28 illustrates a method of page request forwarding for a UE in an ECM-CONNECTED state according to an example embodiment. FIG. 29 illustrates a method of page request forwarding for a UE in ECM-IDLE state according to one example embodiment. FIG. 30 illustrates a method for inactivity registration timer update according to one example embodiment. FIG. 31 illustrates a method for error cases resulting from SIM switching according to one example embodiment. FIG. 32 illustrates a non-roaming architecture for interworking between 5GS and EPS according to one example embodiment. FIG. 33 illustrates another multi-SIM configuration GUI according to an example embodiment. FIG. 34 is a diagram illustrating a UE requesting provisioning of a temporary identifier from a core network according to one example embodiment. FIG. 35 is a diagram illustrating a multi-SIM UE detecting paging collisions according to an example embodiment. FIG. 36 illustrates a procedure for activating and deactivating the registration pause timer according to one example embodiment. FIG. 37 is a diagram illustrating a UE executing a request for the core network to stop paging the UE according to one example embodiment. FIG. 38 is a diagram illustrating a core network providing a notification to a UE indicating a missed page according to one example embodiment. FIG. 39 illustrates a method for a multi-SIM UE to perform indirect registration of an inactive SIM via the user plane of an active SIM according to one example embodiment. FIG. 40 illustrates a method for a multi-SIM UE to receive a NAS notification from PLMN2 for SIM2 via the user plane of PLMN1 according to one example embodiment. FIG. 41 is a diagram illustrating how a multi-SIM UE provides user configuration to the core network with preferences for how the user wants the UE to operate for multi-SIM operation according to one example embodiment.

The areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description of the exemplary embodiments is for illustrative purposes only and therefore does not necessarily limit the scope of the present disclosure.

The Third Generation Partnership Project (3GPP) develops technical standards for cellular communication network technologies, including radio access, core transport networks, and service capabilities, including work on codecs, security, and quality of service. Recent radio access technology (RAT) standards include WCDMA (commonly referred to as 3G), LTE (commonly referred to as 4G), LTE-Advanced standards, and New Radio (NR), also known as "5G". Development of the 3GPP NR standard continues and is expected to include the definition of next-generation radio access technologies (new RATs), which are expected to include the provision of new flexible radio access below 7 GHz, and the provision of new ultra-mobile broadband radio access above 7 GHz. Flexible radio access is expected to consist of new non-backward compatible radio access in new spectrum below 7 GHz and is expected to include different operating modes that can be multiplexed together in the same spectrum to address a broad set of 3GPP NR use cases with different requirements. Ultra Mobile Broadband is expected to include cmWave and mmWave spectrum, providing opportunities for ultra mobile broadband access for indoor applications and hotspots, for example. In particular, ultra mobile broadband is expected to share a common design framework with sub-7 GHz flexible wireless access, with cmWave and mmWave specific design optimizations.

3GPP has identified a variety of use cases that NR is expected to support, resulting in a wide variety of user experience requirements for data rates, latency, and mobility. The use cases include the following general categories: advanced mobile broadband (eMBB) ultra-reliable low-latency communications (URLLC), massive machine-type communications (mMTC), network operations (e.g., network slicing, routing, migration and interworking, energy conservation), and advanced vehicle-to-thing (eV2X) communications, which may include any of vehicle-to-vehicle communications (V2V), vehicle-to-infrastructure communications (V2I), vehicle-to-network communications (V2N), vehicle-to-pedestrian communications (V2P), and vehicle communications with other entities. Specific services and applications in these categories include, for example, surveillance and sensor networks, device remote control, two-way remote control, personal cloud computing, video streaming, wireless cloud-based office, first responder connectivity, vehicle emergency notification, disaster alerts, real-time gaming, multi-party video calling, autonomous driving, augmented reality, haptic internet, virtual reality, home automation, robotics, and aerial drones. All of these use cases, as well as others, are contemplated herein.

The following is a list of acronyms relating to service levels and core network technologies that may appear in the following description. Unless otherwise stated, the acronyms used in this specification refer to the corresponding terms listed below.

Exemplary Communication Systems and Networks
1A illustrates an example communication system 100 in which the systems, methods, and apparatus described and claimed herein may be used. The communication system 100 may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, 102e, 102f, and/or 102g, which may be referred to generally or collectively as WTRUs 102 or WTRUs 102. The communication system 100 may include a radio access network (RAN) 103/104/105/103b/104b/105b, a core network 106/107/109, a public switched telephone network (PSTN) 108, the Internet 110, other networks 112, and network services 113. The network services 113 may include, for example, a V2X server, a V2X function, a ProSe server, a ProSe function, IoT services, video streaming, and/or edge computing.

It will be appreciated that the concepts disclosed herein may be used with any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs 102 may be any type of apparatus or device configured to operate and/or communicate in a wireless environment. In the example of FIG. 1A, each of the WTRUs 102 is illustrated in FIGS. 1A-1E as a handheld wireless communication device. In the wide variety of use cases contemplated for wireless communication, it will be appreciated that each WTRU may comprise or be included in any type of apparatus or device configured to transmit and/or receive wireless signals, including, by way of example only, a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a mobile phone, a personal digital assistant (PDA), a smartphone, a laptop, a tablet, a netbook, a notebook computer, a personal computer, a wireless sensor, a consumer electronic device, a wearable device such as a smart watch or smart clothing, a medical or eHealth device, a robot, an industrial device, a drone, a vehicle such as a car, a bus or a truck, a train, or an airplane, etc.

The communication system 100 may also include a base station 114a and a base station 114b. In the example of FIG. 1A, each base station 114a and 114b is illustrated as a single element. In practice, the base stations 114a and 114b may include any number of interconnected base stations and/or network elements. The base station 114a may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, and 102c to facilitate access to one or more communication networks, such as the core network 106/107/109, the Internet 110, the network services 113, and/or other networks 112. Similarly, the base station 114b may be any type of device configured to interface wired and/or wirelessly with at least one of the remote radio heads (RRHs) 118a, 118b, the transmission and reception points (TRPs) 119a, 119b, and/or the roadside units (RSUs) 120a and 120b to facilitate access to one or more communication networks, such as the core network 106/107/109, the Internet 110, the other networks 112, and/or the network services 113. The RRHs 118a, 118b may be any type of device configured to interface wirelessly with at least one of the WTRUs 102, e.g., the WTRU 102c, to facilitate access to one or more communication networks, such as the core network 106/107/109, the Internet 110, the network services 113, and/or the other networks 112.

The TRPs 119a, 119b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102d, 102e, 102f to facilitate access to one or more communication networks, such as the core network 106/107/109, the Internet 110, the network services 113, and/or other networks 112. The RSUs 120a and 120b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102e, 102f, 102e, 102f to facilitate access to one or more communication networks, such as the core network 106/107/109, the Internet 110, the network services 113, and/or other networks 112. As an example, the base stations 114a, 114b may be a base transceiver station (BTS), a NodeB, an eNodeB, a Home NodeB, a Home eNodeB, a next-generation NodeB (gNodeB), a satellite, a site controller, an access point (AP), a wireless router, etc.

The base station 114a may be part of the RAN 103/104/105, which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC) 2302, a radio network controller (RNC), relay nodes, etc. Similarly, the base station 114b may be part of the RAN 103b/104b/105b, which may also include other base stations and/or network elements (not shown), such as a BSC, an RNC, relay nodes, etc. The base station 114a may be configured to transmit and/or receive wireless signals within a particular geographic area, which may be referred to as a cell (not shown). Similarly, the base station 114b may be configured to transmit and/or receive wired and/or wireless signals within a particular geographic area, which may be referred to as a cell (not shown). The cells may be further divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, for example, the base station 114a may include three transceivers, e.g., one transceiver for each sector of the cell. The base station 114a may employ multiple-input multiple-output (MIMO) technology and thus may utilize multiple transceivers for each sector of the cell, for example.

The base station 114a may communicate with one or more of the WTRUs 102a, 102b, 102c, and 102g via an air interface 115/116/117, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, cmWave, mmWave, etc.). The air interface 115/116/117 may be established using any suitable radio access technology (RAT).

The base station 114b may communicate with one or more of the RRHs 118a and 118b, the TRPs 119a and 119b, and/or the RSUs 120a and 120b via a wired or air interface 115b/116b/117b, which may be any suitable wired (e.g., cable, fiber optic, etc.) or wireless communication link (e.g., RF, microwave, IR, UV, visible light, cmWave, mmWave, etc.). The air interface 115b/116b/117b may be established using any suitable RAT.

The RRHs 118a, 118b, the TRPs 119a, 119b and/or the RSUs 120a, 120b may communicate with one or more of the WTRUs 102c, 102d, 102e, 102f via an air interface 115c/116c/117c, which may be any suitable wireless communication link (e.g., RF, microwave, IR, ultraviolet UV, visible light, cmWave, mmWave, etc.). The air interface 115c/116c/117c may be established using any suitable RAT.

The WTRUs 102 may communicate with each other via a direct air interface 115d/116d/117d, such as sidelink communication, which may be any suitable wireless communication link (e.g., RF, microwave, IR, ultraviolet UV, visible light, cmWave, mmWave, etc.). The air interface 115d/116d/117d may be established using any suitable RAT.

The communication system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base station 114a and WTRUs 102a, 102b, 102c of the RANs 103/104/105, or the RRHs 118a, 118b, TRPs 119a, 119b and/or RSUs 120a and 120b of the RANs 103b/104b/105b and the WTRUs 102c, 102d, 102e, and 102f may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interfaces 115/116/117 and/or 115c/116c/117c, respectively, using Wideband CDMA (WCDMA). WCDMA may include communication protocols such as High Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA can include High Speed Downlink Packet Access (HSDPA) and/or High Speed Uplink Packet Access (HSUPA).

The base station 114a and WTRUs 102a, 102b, 102c, and 102g of RAN 103/104/105, or the RRHs 118a and 118b, TRPs 119a and 119b, and/or RSUs 120a and 120b and WTRUs 102c, 102d of RAN 103b/104b/105b may implement a wireless technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 115/116/117 or 115c/116c/117c, respectively, using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A). Air interface 115/116/117 or 115c/116c/117c may implement 3GPP NR technology. LTE and LTE-A technologies may include LTE D2D and/or V2X technologies and interfaces (e.g., sidelink communications, etc.). Similarly, 3GPP NR technology may include NR V2X technologies and interfaces (e.g., sidelink communications, etc.).

The base station 114a and WTRUs 102a, 102b, 102c, and 102g of RAN 103/104/105, or the RRHs 118a and 118b, TRPs 119a and 119b, and/or RSUs 120a and 120b of RAN 103b/104b/105b, and WTRUs 102c, 102d, 102e, and 102f may be IEEE 802.16 (e.g., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 Wireless technologies such as EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile Communications (GSM) (registered trademark), Enhanced Data Rates for GSM Evolution (EDGE), and GSM EDGE (GERAN) can be implemented.

1A may be, for example, a wireless router, Home NodeB, Home eNodeB, or access point, and may utilize any suitable RAT to facilitate wireless connectivity in a localized area, such as, for example, an office, a home, a vehicle, a train, an aircraft, a satellite, a manufacturing, a campus, etc. The base station 114c and the WTRU 102, for example, the WTRU 102e, may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). Similarly, the base station 114c and the WTRU 102, for example, the WTRU 102d, may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). The base station 114c and the WTRU 102, e.g., the WTRU 102e, may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, NR, etc.) to establish a picocell or femtocell. As shown in FIG. 1A, the base station 114c may have a direct connection to the Internet 110. Thus, the base station 114c may not need to access the Internet 110 via the core network 106/107/109.

RAN 103/104/105 and/or RAN 103b/104b/105b may communicate with a core network 106/107/109, which may be any type of network configured to provide voice, data, messaging, authorization and authentication, application, and/or Voice over Internet Protocol (VoIP) services to one or more of WTRUs 102. For example, the core network 106/107/109 may provide call control, billing services, mobile location-based services, prepaid calls, Internet connectivity, packet data network connectivity, Ethernet connectivity, video distribution, etc., and/or perform high-level security functions such as user authentication.

Although not shown in FIG. 1A, it will be appreciated that RAN 103/104/105 and/or RAN 103b/104b/105b and/or core network 106/107/109 may communicate directly or indirectly with other RANs employing the same RAT as RAN 103/104/105 and/or RAN 103b/104b/105b or a different RAT. For example, core network 106/107/109 may communicate with another RAN (not shown) employing GSM or NR radio technology in addition to being connected to RAN 103/104/105 and/or RAN 103b/104b/105b, which may utilize E-UTRA radio technology.

The core network 106/107/109 may also serve as a gateway for the WTRU 102 to access the PSTN 108, the Internet 110, and/or other networks 112. The PSTN 108 may include a circuit-switched telephone network providing plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communications protocols such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Internet Protocol (IP) in the TCP/IP Internet protocol suite. The other networks 112 may include wired or wireless communications networks owned and/or operated by other service providers. For example, the network 112 may include any type of packet data network (e.g., an IEEE 802.3 Ethernet network), or another core network connected to one or more RANs, which may employ the same RAT as the RANs 103/104/105 and/or RANs 103b/104b/105b or a different RAT.

Some or all of the WTRUs 102a, 102b, 102c, 102d, 102e, and 102f of the communication system 100 may include multi-mode capabilities, e.g., the WTRUs 102a, 102b, 102c, 102d, 102e, and 102f may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU 102g shown in FIG. 1A may be configured to communicate with a base station 114a that may employ a cellular-based wireless technology and with a base station 114c that may employ an IEEE 802 wireless technology.

Although not shown in FIG. 1A, it will be appreciated that the user equipment may have a wired connection to a gateway. The gateway may be a residential gateway (RG). The RG may provide a connection to the core network 106/107/109. It will be appreciated that many of the concepts contained herein may be equally applicable to UEs that are WTRUs and UEs that use a wired connection to connect to a network. For example, the ideas that apply to the radio interfaces 115, 116, 117 and 115c/116c/117c may be equally applicable to a wired connection.

1B is a system diagram of an example RAN 103 and core network 106. As described above, the RAN 103 may employ UTRA radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface 115. The RAN 103 may also communicate with the core network 106. As shown in FIG. 1B, the RAN 103 may include NodeBs 140a, 140b, and 140c, which may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 115. The NodeBs 140a, 140b, and 140c may each be associated with a particular cell (not shown) within the RAN 103. The RAN 103 may also include RNCs 142a, 142b. It will be appreciated that the RAN 103 may include any number of Node Bs and Radio Network Controllers (RNCs).

As shown in FIG. 1B, NodeBs 140a, 140b can communicate with RNC 142a. Additionally, NodeB 140c can communicate with RNC 142b. NodeBs 140a, 140b, and 140c can communicate with their respective RNCs 142a and 142b via an Iub interface. RNCs 142a and 142b can communicate with each other via an Iur interface. Each of RNCs 142a and 142b can be configured to control its respective NodeB 140a, 140b, and 140c. Additionally, each of RNCs 142a and 142b may be configured to perform or support other functions such as outer loop power control, load control, admission control, packet scheduling, handover control, macro diversity, security functions, data encryption, etc.

The core network 106 shown in FIG. 1B may include a media gateway (MGW) 144, a mobile switching center (MSC) 146, a serving GPRS support node (SGSN) 148, and/or a gateway GPRS support node (GGSN) 150. Although each of the foregoing elements is illustrated as part of the core network 106, it will be understood that any one of these elements may be owned and/or operated by an entity other than the core network operator.

The RNC 142a of the RAN 103 may be connected to the MSC 146 of the core network 106 via an IuCS interface. The MSC 146 may be connected to the MGW 144. The MSC 146 and MGW 144 may provide the WTRUs 102a, 102b, and 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, and 102c and traditional terrestrial communications devices.

The RNC 142a of the RAN 103 may also be connected to the SGSN 148 of the core network 106 via an IuPS interface. The SGSN 148 may be connected to the GGSN 150. The SGSN 148 and the GGSN 150 may provide the WTRUs 102a, 102b, and 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, and 102c and IP-enabled devices.

The core network 106 may also be connected to other networks 112, which may include other wired or wireless networks owned and/or operated by other service providers.

1C is a system diagram of an example RAN 104 and core network 107. As described above, the RAN 104 may employ E-UTRA radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface 116. The RAN 104 may also communicate with the core network 107.

RAN 104 may include eNodeBs 160a, 160b, and 160c, although it will be appreciated that RAN 104 may include any number of eNodeBs. eNodeBs 160a, 160b, and 160c may each include one or more transceivers for communicating with WTRUs 102a, 102b, and 102c over the air interface 116. For example, eNodeBs 160a, 160b, and 160c may implement MIMO technology. Thus, eNodeB 160a may use multiple antennas to transmit wireless signals to and receive wireless signals from, for example, WTRU 102a.

Each of the eNodeBs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users on the uplink and/or downlink, etc. As illustrated in FIG. 1C, the eNodeBs 160a, 160b, 160c may communicate with each other via an X2 interface.

The core network 107 shown in FIG. 1C may include a mobility management gateway (MME) 162, a serving gateway 164, and a packet data network (PDN) gateway 166. Although each of the foregoing elements is illustrated as part of the core network 107, it will be understood that any one of these elements may be owned and/or operated by an entity other than the core network operator.

The MME 162 may be connected to each of the eNodeBs 160a, 160b, and 160c of the RAN 104 via an S1 interface and may function as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, and 102c, activating/deactivating bearers, selecting a particular serving gateway during initial attachment of the WTRUs 102a, 102b, and 102c, and the like. The MME 162 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) employing other radio technologies such as GSM or WCDMA.

The serving gateway 164 may be connected to each of the eNodeBs 160a, 160b, and 160c of the RAN 104 via an S1 interface. The serving gateway 164 may generally route and forward user data packets to and from the WTRUs 102a, 102b, and 102c. The serving gateway 164 may also perform other functions such as anchoring the user plane during inter-eNodeB handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, and 102c, managing and storing the context of the WTRUs 102a, 102b, and 102c.

The serving gateway 164 may also be connected to a PDN gateway 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

The core network 107 may facilitate communications with other networks. For example, the core network 107 may provide the WTRUs 102a, 102b, and 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, and 102c and traditional terrestrial communications devices. For example, the core network 107 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that serves as an interface between the core network 107 and the PSTN 108. In addition, the core network 107 may provide the WTRUs 102a, 102b, and 102c with access to the networks 112, which may include other wired or wireless networks owned and/or operated by other service providers.

FIG. 1D is a system diagram of an example RAN 105 and core network 109. RAN 105 may employ NR radio technology to communicate with WTRUs 102a and 102b over air interface 117. RAN 105 may also communicate with core network 109. Non-3GPP Interworking Function (N3IWF) 199 may employ non-3GPP radio technology to communicate with WTRU 102c over air interface 198. N3IWF 199 may also communicate with core network 109.

RAN 105 may include gNodeBs 180a and 180b. It will be appreciated that RAN 105 may include any number of gNodeBs. gNodeBs 180a and 180b may each include one or more transceivers for communicating with WTRUs 102a and 102b over air interface 117. When integrated access and backhaul connectivity is used, the same air interface may be used between the WTRUs and gNodeBs, which may be the core network 109 via one or more gNBs. gNodeBs 180a and 180b may implement MIMO, MU-MIMO, and/or digital beamforming techniques. Thus, gNodeB 180a may use multiple antennas to transmit wireless signals to and receive wireless signals from WTRU 102a, for example. It should be appreciated that the RAN 105 may employ other types of base stations, such as, for example, eNodeBs. It should also be understood that the RAN 105 may employ multiple types of base stations. For example, the RAN may employ eNodeBs and gNodeBs.

The N3IWF 199 may include a non-3GPP access point 180c. It will be appreciated that the N3IWF 199 may include any number of non-3GPP access points. The non-3GPP access point 180c may include one or more transceivers for communicating with the WTRU 102c over the air interface 198. The non-3GPP access point 180c may use 802.11 protocols for communicating with the WTRU 102c over the air interface 198.

Each of gNodeBs 180a and 180b may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users on the uplink and/or downlink, etc. As shown in FIG. 1D, gNodeBs 180a and 180b may communicate with each other, for example, via an Xn interface.

The core network 109 shown in FIG. 1D may be a 5G core network (5GC). The core network 109 may provide a number of communication services to customers interconnected by a radio access network. The core network 109 includes several entities that perform the functions of a core network. As used herein, the term "core network entity" or "network function" refers to any entity that performs one or more functions of a core network. It is understood that such a core network entity may be a logical entity implemented in the form of computer-executable instructions (software) stored in a memory and executed on a processor of a device or computer system configured for wireless and/or network communication, such as the system 90 shown in FIG. 1G.

In the example of FIG. 1D, the 5G core network 109 may include an Access and Mobility Management Function (AMF) 172, a Session Management Function (SMF) 174, a User Plane Function (UPF) 176a and 176b, a User Data Management Function (UDM) 197, an Authentication Server Function (AUSF) 190, a Network Publishing Function (NEF) 196, a Policy Control Function (PCF) 184, a Non-3GPP Interworking Function (N3IWF) 199, and a User Data Repository (UDR) 178. Although each of the aforementioned elements is illustrated as part of the 5G core network 109, it will be understood that any one of these elements may be owned and/or operated by an entity other than the core network operator. It will also be understood that the 5G core network may not be comprised of all of these elements, may be comprised of additional elements, and may be comprised of multiple instances of each of these elements. Although FIG. 1D shows the network functions directly connected to each other, it should be understood that the network functions can communicate through a routing agent, such as a diameter routing agent or a message bus.

In the example of FIG. 1D, connections between network functions are achieved through a set of interfaces or reference points. It will be appreciated that network functions may be modeled, described, or implemented as a set of services that are invoked or called by other network functions or services. Invocation of network function services may be achieved through direct connections between network functions, messaging exchanges on a message bus, software function calls, etc.

The AMF 172 may be connected to the RAN 105 via an N2 interface and may function as a control node. For example, the AMF 172 may be responsible for registration management, connection management, reachability management, access authentication, and access authorization. The AMF may be responsible for forwarding user plane tunnel configuration information to the RAN 105 via the N2 interface. The AMF 172 may receive user plane tunnel configuration information from the SMF via the N11 interface. The AMF 172 may generally route and forward NAS packets to and from the WTRUs 102a, 102b, and 102c via the N1 interface. The N1 interface is not shown in FIG. 1D.

The SMF 174 may be connected to the AMF 172 via an N11 interface. Similarly, the SMF may be connected to the PCF 184 via an N7 interface and to the UPFs 176a and 176b via an N4 interface. The SMF 174 may function as a control node. For example, the SMF 174 may be responsible for session management, IP address allocation for the WTRUs 102a, 102b, and 102c, management and configuration of traffic steering rules in the UPFs 176a and 176b, and generation of downlink data notifications to the AMF 172.

The UPF 176a and the UPF 176b may provide the WTRUs 102a, 102b, and 102c with access to a packet data network (PDN), such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, and 102c and other devices. The UPF 176a and the UPF 176b may also provide the WTRUs 102a, 102b, and 102c with access to other types of packet data networks. For example, the other network 112 may be an Ethernet network or any type of network that exchanges packets of data. The UPF 176a and the UPF 176b may receive traffic steering rules from the SMF 174 via the N4 interface. The UPF 176a and the UPF 176b may provide access to a packet data network by connecting the packet data network with the N6 interface or by connecting with each other and other UPFs via the N9 interface. In addition to providing access to the packet data network, the UPF 176 may be responsible for packet routing and forwarding, policy rule enforcement, quality of service handling for user plane traffic, and downlink packet buffering.

The AMF 172 may also be connected to the N3IWF 199, for example, via an N2 interface. The N3IWF facilitates connectivity between the WTRU 102c and the 5G core network 170, for example, via an air interface technology not defined by 3GPP. The AMF may interact with the N3IWF 199 in the same or similar manner as it interacts with the RAN 105.

The PCF 184 may be connected to the SMF 174 via an N7 interface, to the AMF 172 via an N15 interface, and to the application function (AF) 188 via an N5 interface. The N15 and N5 interfaces are not shown in FIG. 1D. The PCF 184 may provide policy rules to control plane nodes such as the AMF 172 and the SMF 174, allowing the control plane nodes to enforce these rules. The PCF 184 may send policies for the WTRUs 102a, 102b, and 102c to the AMF 172 so that the AMF may distribute the policies to the WTRUs 102a, 102b, and 102c via the N1 interface. The policies may then be enforced or applied at the WTRUs 102a, 102b, and 102c.

The UDR 178 can act as a repository of authentication credentials and subscription information. The UDR can connect to network functions so that the network functions can add, read, and modify data in the repository. For example, the UDR 178 can connect to the PCF 184 via an N36 interface. Similarly, the UDR 178 can connect to the NEF 196 via an N37 interface, and the UDR 178 can connect to the UDM 197 via an N35 interface.

The UDM 197 may act as an interface between the UDR 178 and other network functions. The UDM 197 may allow access of the UDR 178 to the network functions. For example, the UDM 197 may connect to the AMF 172 via an N8 interface, and the UDM 197 may connect to the SMF 174 via an N10 interface. Similarly, the UDM 197 may connect to the AUSF 190 via an N13 interface. The UDR 178 and the UDM 197 may be tightly integrated.

AUSF190 performs authentication related operations and connects to UDM178 via the N13 interface and to AMF172 via the N12 interface.

The NEF 196 exposes the capabilities and services of the 5G core network 109 to the application functions (AFs) 188. The exposure may be done over the N33 API interface. The NEF can connect to the AF 188 via the N33 interface and can connect to other network functions to expose the capabilities and services of the 5G core network 109.

The application functions 188 can interact with the network functions of the 5G core network 109. The interaction between the application functions 188 and the network functions may occur through a direct interface or through the NEF 196. The application functions 188 may be considered part of the 5G core network 109 or may be external to the 5G core network 109 and deployed by a company that has a business relationship with the mobile network operator.

Network slicing is a mechanism that can be used by mobile network operators to support one or more "virtual" core networks behind the operator's air interface. It involves "slicing" the core network into one or more virtual networks to support different RANs or different service types running over a single RAN. Network slicing allows operators to create customized networks to provide optimized solutions for different market scenarios that demand diverse requirements, for example in the areas of functionality, performance and isolation.

3GPP is designing the 5G core network to support network slicing. Network slicing is a great tool that network operators can use to support a diverse set of 5G use cases (e.g., large-scale IoT, critical communications, V2X, and advanced mobile broadband) that demand very different and sometimes extreme requirements. Without network slicing technology, the network architecture is likely not flexible and scalable enough to efficiently support the needs of a wider range of use cases, when each use case has its own specific set of performance, scalability, and availability requirements. In addition, the introduction of new network services needs to become more efficient.

Referring again to FIG. 1D, in a network slicing scenario, the WTRU 102a, 102b, or 102c may be connected to the AMF 172 via an N1 interface. The AMF may be logically part of one or more slices. The AMF may coordinate the connection or communication of the WTRU 102a, 102b, or 102c with one or more UPFs 176a and 176b, SMF 174, and other network functions. Each of the UPFs 176a and 176b, SMF 174, and other network functions may be part of the same slice or different slices. When they are part of different slices, they may be separated from each other in the sense that they may utilize different computing resources, security credentials, etc.

The core network 109 may facilitate communication with other networks. For example, the core network 109 may include or communicate with an IP gateway, such as an IP Multimedia Subsystem (IMS) server, that serves as an interface between the 5G core network 109 and the PSTN 108. For example, the core network 109 may include or communicate with a short message service (SMS) service center that facilitates communication via short message service. For example, the 5G core network 109 may facilitate the exchange of non-IP data packets between the WTRUs 102a, 102b, and 102c and a server or application function 188. In addition, the core network 170 may provide the WTRUs 102a, 102b, and 102c with access to the network 112, which may include other wired or wireless networks owned and/or operated by other service providers.

The core network entities described herein and shown in Figures 1A, 1C, 1D, and 1E are identified by the names given to those entities in certain existing 3GPP specifications, but it is understood that in the future, those entities and functions may be identified by other names and that certain entities or functions may be combined in future specifications published by 3GPP, including future 3GPP NR specifications. Thus, it is understood that the specific network entities and functions described and shown in Figures 1A, 1B, 1C, 1D, and 1E are provided by way of example only, and that the subject matter disclosed and claimed herein may be practiced or implemented in any similar communication system, whether currently defined or defined in the future.

1E illustrates an example communication system 111 in which the systems, methods, and apparatus described herein may be used. The communication system 111 may include wireless transmit/receive units (WTRUs) A, B, C, D, E, F, a base station gNB 121, a V2X server 124, and roadside units (RSUs) 123a and 123b. In practice, the concepts presented herein may be applied to any number of WTRUs, base stations gNBs, V2X networks, and/or other network elements. One or some or all of WTRUs A, B, C, D, E, and F may be outside the range of the access network coverage 122. WTRUs A, B, and C form a V2X group, of which WTRU A is the group lead and WTRUs B and C are group members.

WTRUs A, B, C, D, E, F can communicate with each other via Uu interface 129b through gNB 121 when they are under access network coverage (only B and F are shown under network coverage in FIG. 1E). WTRUs A, B, C, D, E, F can communicate with each other directly via sidelink (PC5 or NR PC5) interfaces 125a, 125b, 128 when they are under or outside of access network coverage (e.g., A, C, WTRUs A, B, C, D, E, F can communicate with each other, and D and E are shown out of network coverage in FIG. 1E).

WTRUs A, B, C, D, E, and F may communicate with the RSU 123a or 123b via a vehicle-to-network (V2N) 126 or sidelink interface 125b. WTRUs A, B, C, D, E, and F may communicate with the V2X server 124 via a vehicle-to-infrastructure (V2I) interface 127. WTRUs A, B, C, D, E, and F may communicate with another UE via a vehicle-to-personal (V2P) interface 128.

1F is a block diagram of an exemplary apparatus or device WTRU 102 that may be configured for wireless communication and operation with the systems, methods, and apparatus described herein, such as the WTRU 102 of FIG. 1A, FIG. 1B, FIG. 1C, FIG. 1D, or FIG. 1E. As shown in FIG. 1F, the exemplary WTRU 102 may include a processor 118, a transceiver 120, a transmit/receive element 122, a speaker/microphone 124, a keypad 126, a display/touchpad/indicators 128, a non-removable memory 130, a removable memory 132, a power source 134, a Global Positioning System (GPS) chipset 136, and other peripherals 138. It will be appreciated that the WTRU 102 may include any subcombination of the foregoing elements. Additionally, the base stations 114a and 114b may represent, and/or may include some or all of the elements illustrated in FIG. 1F and described herein, such as, but not limited to, a transceiver station (BTS), a NodeB, a site controller, an access point (AP), a Home NodeB, an evolved Home NodeB (eNodeB), a Home evolved NodeB (HeNB), a Home evolved NodeB gateway, a next generation NodeB (gNodeB), and a proxy node, among others.

The processor 118 may be a general-purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), a state machine, etc. The processor 118 may perform signal coding, data processing, power control, input/output processing, and/or any other function that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit/receive element 122. Although FIG. 1F illustrates the processor 118 and the transceiver 120 as separate components, it will be understood that the processor 118 and the transceiver 120 may be integrated into an electronic package or chip.

The transmit/receive element 122 of the UE may be configured to transmit or receive signals to or from a base station (e.g., base station 114a of FIG. 1A) via air interface 115/116/117, or another UE via air interface 115d/116d/117d. For example, the transmit/receive element 122 may be an antenna configured to transmit and/or receive RF signals. The transmit/receive element 122 may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. The transmit/receive element 122 may be configured to transmit and receive both RF and light signals. It will be appreciated that the transmit/receive element 122 may be configured to transmit and/or receive any combination of wireless or wired signals.

In addition, although the transmit/receive element 122 is illustrated in FIG. 1F as a single element, the WTRU 102 may include any number of transmit/receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, the WTRU 102 may include two or more transmit/receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 115/116/117.

The transceiver 120 may be configured to modulate signals transmitted by the transmit/receive element 122 and demodulate signals received by the transmit/receive element 122. As mentioned above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate via multiple RATs, e.g., NR and IEEE 802.11 or NR and E-UTRA, or to enable the WTRU 102 to communicate with the same RAT via multiple beams to different RRHs, TRPs, RSUs, or nodes.

The processor 118 of the WTRU 102 may be coupled to and receive user input data from a speaker/microphone 124, a keypad 126, and/or a display/touchpad/indicator 128 (e.g., a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker/microphone 124, the keypad 126, and/or the display/touchpad/indicator 128. In addition, the processor 118 may access information from and store data in any type of suitable memory, such as a non-removable memory 130 and/or a removable memory 132. The non-removable memory 130 may include a random access memory (RAM), a read only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, or the like. The processor 118 may access information from and store data in memory that is not physically located on the WTRU 102, such as on a server hosted on a cloud or edge computing platform or a home computer (not shown).

The processor 118 may receive power from the power source 134 and may be configured to distribute and/or control the power to other components of the WTRU 102. The power source 134 may be any suitable device for providing power to the WTRU 102. For example, the power source 134 may include one or more dry batteries, solar cells, fuel cells, etc.

The processor 118 may also be coupled to a GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to or instead of information from the GPS chipset 136, the WTRU 102 may receive location information from a base station (e.g., base stations 114a, 114b) over the air interface 115/116/117 and/or determine its location based on the timing of signals received from two or more nearby base stations. It will be appreciated that the WTRU 102 may obtain location information by any suitable location determination method.

The processor 118 may further be coupled to other peripherals 138, which may include one or more software and/or hardware modules that provide additional features, functionality, and/or wired or wireless connectivity. For example, the peripherals 138 may include various sensors, such as an accelerometer, a biometric (e.g., fingerprint) sensor, an e-compass, a satellite transceiver, a digital camera (for photos or videos), a Universal Serial Bus (USB) port or other interconnection interface, a vibration device, a television transceiver, a hands-free headset, a Bluetooth® module, a frequency modulation (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like.

The WTRU 102 may be included in other apparatus or devices, such as sensors, appliances, wearable devices such as smart watches or smart clothing, medical or eHealth devices, robots, industrial equipment, drones, vehicles such as automobiles, trucks, trains, or airplanes. The WTRU 102 may be connected to other components, modules, or systems of such apparatus or devices via one or more interconnection interfaces, such as an interconnection interface that may include one of the peripherals 138.

1G is a block diagram of an exemplary computing system 90 that may embody one or more devices of the communications networks shown in FIGS. 1A, 1C, 1D, and 1E, such as particular nodes or functional entities of RAN 103/104/105, core network 106/107/109, PSTN 108, Internet 110, other networks 112, or network services 113. The computing system 90 may comprise a computer or server and may be controlled primarily by computer-readable instructions, which may be in the form of software, regardless of where or how such software is stored or accessed. Such computer-readable instructions may be executed within a processor 91 to cause the computing system 90 to perform operations. The processor 91 may be a general-purpose processor, a special-purpose processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), a state machine, etc. The processor 91 may perform signal coding, data processing, power control, input/output processing, and/or any other function that enables the computing system 90 to operate in a communications network. The coprocessor 81 is an optional processor different from the main processor 91 that may perform additional functions or assist the processor 91. The processor 91 and/or the coprocessor 81 may receive, generate, and process data related to the methods and apparatus disclosed herein.

During operation, the processor 91 fetches, decodes, and executes instructions and transfers information to and from other resources via a system bus 80, which is the computing system's main data transfer path. Such a system bus connects the components of the computing system 90 and defines the medium for data exchange. A system bus 80 typically includes data lines for transmitting data, address lines for transmitting addresses, and control lines for transmitting interrupts and operating the system bus. One example of such a system bus 80 is a PCI (Peripheral Component Interconnect) bus.

The memories coupled to the system bus 80 include random access memory (RAM) 82 and read only memory (ROM) 93. Such memories include circuits that allow information to be stored and retrieved. ROM 93 generally includes stored data that cannot be easily altered. Data stored in RAM 82 may be read or altered by the processor 91 or other hardware devices. Access to RAM 82 and/or ROM 93 may be controlled by a memory controller 92. The memory controller 92 may provide an address translation function that converts virtual addresses to physical addresses when instructions are executed. The memory controller 92 may also provide a memory protection function that separates processes in the system and separates system processes from user processes. Thus, a program executing in the first mode can only access memory mapped by its own process virtual address space and cannot access memory in another process' virtual address space unless memory sharing between processes is set up.

In addition, the computing system 90 may include a peripheral controller 83 that serves to communicate instructions from the processor 91 to peripheral devices such as a printer 94, a keyboard 84, a mouse 95, and a disk drive 85.

The display 86, controlled by the display controller 96, is used to display visual output generated by the computing system 90. Such visual output may include text, graphics, animated graphics, and video. The visual output may be provided in the form of a graphical user interface (GUI). The display 86 may be implemented with a CRT-based video display, an LCD-based flat panel display, a gas plasma-based flat panel display, or a touch panel. The display controller 96 contains the electronic components necessary to generate the video signals sent to the display 86.

Furthermore, the computing system 90 may include communications circuitry, such as, for example, a wireless or wired network adapter 97, that may be used to connect the computing system 90 to external communications networks or devices, such as the RANs 103/104/105, core networks 106/107/109, PSTN 108, Internet 110, WTRU 102, or other networks 112 of Figures 1A, 1B, 1C, 1D, and 1E, to enable the computing system 90 to communicate with other nodes or functional entities of those networks. The communications circuitry may be used alone or in combination with the processor 91 to perform the transmission and reception steps of a particular apparatus, node, or functional entity described herein.

It is understood that any or all of the devices, systems, methods, and processes described herein may be embodied in the form of computer-executable instructions (e.g., program code) stored on a computer-readable storage medium, which, when executed by a processor, such as processor 118 or 91, causes the processor to execute and/or perform the systems, methods, and processes described herein. Specifically, any of the steps, operations, or functions described herein may be embodied in the form of such computer-executable instructions executed on a processor of a device or computing system configured for wireless and/or wired network communication. Computer-readable storage media include volatile and non-volatile, removable and non-removable media implemented in any non-transitory (e.g., tangible or physical) method or technology for storing information, although such computer-readable storage media do not include signals. Computer-readable storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVDs) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other tangible or physical medium that can be used to store the desired information and that can be accessed by a computing system.

(5G System Architecture)
Figure 2 shows the 3GPP 5G non-roaming system architecture where various entities interact with each other via the indicated reference points. User Equipment (UE) 102 can communicate with the Core Network (CN) to establish control signaling and enable the UE 102 to use services from the CN. Examples of control signaling functions are registration, attachment and mobility management, authentication and authorization, session management, etc.

The following Network Functions (NFs) in FIG. 2 are the main NFs in the control plane (CP) of the CN that are involved in control signaling:
Access and Mobility Function (AMF) 172: The UE 102 sends N1 messages via the RAN node 105 to the AMF 172 to perform many control plane signaling such as registration, attachment management, mobility management, access authentication and authorization, etc.
Session Management Function (SMF) 174: The SMF 174 is responsible for session management related to establishing PDU sessions to enable the UE to send data to a Data Network (DN) 208 such as the Internet or an application server and other session management related functions.
Policy and Control Function (PCF) 184: The PCF 184 provides a policy framework that manages network behavior, accesses subscription information, makes policy decisions, and so on.
Authentication Server Function (AUSF) 190: The AUSF 190 supports authentication of UEs for 3GPP and untrusted non-3GPP access.
Unified Data Management (UDM) 197: The UDM 197 supports 3GPP AKA authentication credential generation, user identification handling, subscription management, etc.
Network Slice Selection Function (NSSF) 216: The NSSF 216 is responsible for aspects of network slice management such as selection of a network slice instance for a UE, management of NSSAI, etc.
Radio Access Network (RAN) 105: The RAN node 105 provides communication access from the UE 102 to the core network, for both control and user plane communications.

(5G Roaming Architecture)
3 illustrates a 5G system roaming architecture for a local breakout scenario in a service-based representation, where the VPLMN is the visited PLMN and the HPLMN is the home PLMN. A Security Edge Protection Proxy (SEPP) 304 enables communication between the VPLMN and the HPLMN.

Figure 4 shows the 5G system roaming architecture for a local breakout scenario in a reference point representation. In this figure, the SEPP is not shown for clarity. The AMF of the VPLMN can communicate with the AUSF of the HPLMN over the N12 interface to authenticate the UE from the HPLMN. Policy information may be communicated between the vPCF and the hPCF over the N24 interface.

(5G registration procedure)
Before a UE can use the services provided by the CN, the UE needs to register with the core network. Figure 5 shows the 5G general registration procedure from TS 23.502 [2] that the UE performs to register with the CN. The following are noteworthy steps of the general registration procedure:
In step S500, the UE provides a registration type to indicate what the request is for. Two common types are initial registration, performed by the UE to initially establish registration with the CN, and periodic registration update, performed at periodic intervals to inform the CN that the UE is still present. In addition, the UE can provide the CN with an identifier, such as a SUCI, that the CN uses to authenticate the UE in step S510 during initial registration.
In steps S502, S504, S506, and S508, the AMF may obtain the SUCI of the UE if not provided in step S500.
In step S510, the AUSF authenticates the UE based on the subscription information provided by the UDM and the SUCI provided by the UE.
In step S512, the AMF returns a registration accept message to the UE indicating the result of the registration procedure. In the case of initial registration, the accept message includes a temporary identifier such as 5G-GUTI, a list of allowed network slices, DRX parameters, and other relevant data for UE operation. The 5G-GUTI identifier includes a 5G-S-TMSI identifier used to identify a paging request for the UE.

(Registration, Attachment, and Radio Resource Control Management States)
In 5GS, the UE maintains management states to enable communication with the core network. These management states consist of registered (RM), connected (CM), and radio resource control (RRC) management states. The management states are maintained in both the UE and the RAN/CN.

For the UE to use the services offered by the CN, the UE needs to register with the CN by performing an initial registration procedure. Once registered, the UE goes from RM-DEREGISTERED state to RM-REGISTERED state as shown in Figure 6. The UE needs to perform periodic registration updates to maintain the RM-REGISTERED state with the network. When the UE is in RM-DEREGISTERED state, the UE cannot access the services offered by the CN.

The Connection Management (CM) state shown in Figure 7 represents the NAS signaling connection between the UE and the AMF over the N1 interface. This signaling connection enables the UE and the CN to communicate information over the control plane for efficient communication in the 5G system.

Finally, the UE also maintains RRC states with RAN nodes, as described in TS 38.300 [4] as follows:
RRC_IDLE: In this state the UE performs PLMN selection, receives broadcast system information, and performs cell reselection. In addition, the UE can enter discontinuous reception (DRX) mode and monitors paging requests from 5GC.
RRC_INACTIVE: In this state the UE performs functions similar to those of RRC_IDLE, except for the fact that paging requests are initiated by the RAN node. In addition, the UE and the RAN node maintain context information that allows the UE to quickly transition to the RRC_CONNECTED state. When in this state, both the control plane connection and the user plane connection between the RAN node and the 5GC are established for the UE.
RRC_CONNECTED: The transfer of unicast data to and from the UE is enabled when the UE is in this state, since both CP and UP are established between the RAN node and the CN for the UE, and other context information is held between the UE and the RAN node to enable communication.

(5G paging mechanism)
Paging refers to a 5GS mechanism by which either the core network or the RAN informs a UE in CM-IDLE or RRC_IDLE/RRC_INACTIVE of pending data destined for the UE. TS 38.304 [5] provides a description of a UE using discontinuous reception (DRX) when in RRC_IDLE and RRC_INACTIVE states to reduce power consumption during periods of inactivity. The UE monitors paging occasions (POs) during DRX to be informed of activity in the CN that may require the UE to establish a connection. The UE makes a calculation based on information provided by the system information received by the UE and the UE_ID to know when to monitor paging occasions. The UE_ID is calculated from an identifier for the UE, such as the IMSI or 5G-S-TMSI, by modulo arithmetic of the identifier to 1024. On the network side, paging works in 5G similarly to the LTE paging shown in FIG. 23.

(identifier)
Section 5.9.4 of H.23.501 describes the 5G Globally Unique Identifier (5G-GUTI).
5G-GUTI is configured as follows.
<5G-GUTI>:=<GUAMI><5G-TMSI>
Here, GUAMI identifies the assigned AMF, and 5G-TMSI uniquely identifies the UE within the AMF.
The Globally Unique AMF ID (GUAMI) shall be constructed as follows:
<GUAMI>:=<MCC><MNC><AMF Region ID><AMF Set ID><AMFPointer>
The AMF Region ID identifies the region, the AMF Set ID uniquely identifies the AMF Set within the AMF region, and the AMF Pointer uniquely identifies the AMF within the AMF set.
NOTE 1: The AMF Region ID addresses the case where there are more AMFs in a network than can be supported by the AMF Set ID and AMF Pointer, by allowing an operator to reuse the same AMF Set ID and AMF Pointer in different regions.
NOTE 2: For details on the structure of the GUAMI fields, see TS 23.003 [19].
The 5G-S-TMSI is a shortened form of the GUTI to enable more efficient over-the-air signaling procedures (e.g., during paging and service requests) and is defined as follows:
<5G-S-TMSI>:=<AMF Set ID><AMFPointer><5G-TMSI>

(Slice-specific authentication and authorization)
In Release 16 of the 5G system, 3GPP agreed to add slice-specific authentication and authorization functionality. This procedure allows the network to initiate an EAP-based procedure with the UE when the UE attempts to register to a specific slice (i.e., S-NSSAI). The EAP-based authentication procedure is based on the UE providing a user identity and associated network credentials in order to be authorized to access the slice. The new procedure is described in References [7] and [8] and is shown in Figure 8. Figure 8 is copied from Reference [8].

(LTE System Architecture)
Figure 19 shows a 3GPP EPS non-roaming system architecture in which a User Equipment (UE) communicates with a Core Network (CN) via an E-UTRAN 3202 to obtain Internet services or other operator services such as IMS. The E-UTRAN is a Random Access Network (RAN) that interfaces with the UE via an LTE-Uu interface. The UE accesses the CN by using NAS signaling via the E-UTRAN via the S1-MME interface and transmits and receives data via the E-UTRAN via the S1-U interface.

The following Network Functions (NF) in FIG. 19 are briefly described below.
Mobility Management Entity (MME): The MME provides NAS signalling to the UE and authenticates and authorises the UE to access the CN whilst managing UE mobility amongst the many functions it performs.
- Home Subscriber Server (HSS) 2000: The HSS 2000 provides authentication/authorization of the UE as well as stores the UE's subscription information.
Serving Gateway (S-GW) 2002: The S-GW 2002 acts as a mobility anchor point for the UEs in the User Plane (UP), routing and forwarding traffic to and from the P-GW.
PDN Gateway (P-GW) 2004: The P-GW 2004 assigns IP addresses to UEs and provides them with access to packet data networks such as the Internet.
Policy and Charging Rules Function (PCRF) 2006: The policy and charging element of the core network.

(LTE Attach Procedure)
The UE performs an attach procedure in order to register with the core network and to use services from the core network that require registration. Figure 20 illustrates the attach procedure, and some notable steps are highlighted below in relation to the initial attach.
In step S2000, the UE sends an attach request to the CN via the eNodeB. In the request, the UE provides an identifier (IMSI), an attach type, UE core network capabilities, UE-specific DRX parameters, preferred network behavior, and other message parameters as described in [9].
In step S2002, the eNodeB selects an appropriate MME and forwards the request to the selected MME.
In steps S2004a and S2004b, the MME performs authentication and NAS security setup to activate the mandatory integrity protection and NAS ciphering. The MME communicates with the HSS to complete this step. From this point on, NAS signaling is protected for both integrity and ciphering.
In step S2006, the MME returns an attach accept to the attach request, including the GUTI, TAI list, session management request information, supported network behavior, service gap time, and other message parameters as specified in [9].
In step S2008, the eNodeB returns an attach accept message to the UE, and the UE stores the message parameters for future use. There may also be associated RRC signaling.
In step S2010, the UE returns a direct transfer message including the Attach Complete message. The eNodeB forwards the Attach Complete message to the MME in step S2012.

EPS Mobility Management and Attachment Management State
The EPS Mobility Management (EMM) states are shown in Figure 21. The UE is initially in EMM-DEREGISTERED state and enters EMM-REGISTERED state after successful connection to the network. Once registered, the UE can use services offered by the network, such as connecting to the Internet and making IMS calls. The UE can stay in EMM-REGISTERED state by performing a Tracking Area Update (TAU) procedure and can enter EMM-DEREGISTERED state by performing a Detach procedure.

The EPS connection management states are shown in Figure 22. These states indicate the state of the NAS signaling connection between the UE and the core network. In ECM-IDLE, the UE has no NAS signaling connection and performs cell and PLMN selection. The transition from ECM-IDLE to ECM-CONNECTED state is done for the following procedures: Attach request, Tracking area update, Service request, and Detach request.

LTE Paging and Service Request
When the UE 102 is in ECM-IDLE state and data is available in the core network of the UE 102, the MME 162 sends a paging request to the UE 102 as shown in Figure 23. The UE 102 can then connect to the core network to receive data associated with the page after performing a service request procedure. The S-GW 2002 then stops paging the UE 102 and the downlink data is forwarded to the UE 102 via the user plane. TS 36.304 [5] describes the calculation of paging occasions for UEs in discontinuous reception (DRX) and how the paging occasions are calculated based on the UE's identity. Based on the calculation, two UEs may have the same paging occasion and monitor paging messages at the same time. The paging message identifies the recipient of the page using the associated UE identity.

(Problem statement)
UEs with multiple USIMs can be applied to various use cases that take advantage of having registrations with more than one operator network. TR 22.834 [6] of the 3GPP SA1 working group's MUSIM study highlights scenarios where use cases involving multiple USIMs may exist. This disclosure focuses on the case where the UE is equipped with common radio and baseband components to support multiple USIMs. Thus, the radio and baseband components may not be dedicated to a single USIM. This disclosure also provides a solution for dual Rx, single Tx UEs, which are within the scope of the MUSIM study.

The MUSIM SA1 study highlights the potential requirements of multiple USIM UEs. Some of these requirements are:
Support for UEs with multiple USIMs in 3GPP systems Support for Single Rx, Single Tx and Dual Rx, Single Tx UE implementations MUSIM UE to allow users to configure preferences for services from multiple USIMs
3GPP systems need to support MUSIM UEs with multiple USIMs from the same or different operators 3GPP systems to indicate the type of traffic to the MUSIM UE that triggered the paging procedure 3GPP systems shall be able to suspend active communication and resume suspended communication in communication with multiple USIM UEs 3GPP systems shall minimize paging collisions for paging with multiple USIM UEs 3GPP systems shall minimize signaling overhead by supporting multiple USIMs MUSIM UEs need to be supported in both 5G and LTE systems It is noted that the terms SIM and USIM (as utilized in TR 22.834 [6]) are used interchangeably in this disclosure. Additionally, the term Multi-SIM is used to refer to multiple USIMs. It is also noted that the terms LTE and EPS are used interchangeably in this disclosure.

(Use case 1)
A user is traveling internationally from the United States to Asia and has a UE that supports multiple USIMs. For cost reduction purposes, the UE is implemented with common radio and baseband components to which the USIMs share access. As a result, only one USIM can be active at a time. The user purchases a USIM upon arrival to access cellular services while traveling within the destination country. The mobile USIM provides services for local voice, text, and high speed data, while the home USIM is primarily used to provide voice and text that the user may want to receive from family and friends while traveling.

(Use case 2)
Another prominent use case utilizing multiple USIMs centers around a user who has both business and personal subscription services and wants to use both services on the same device. The user has an enterprise issued UE with a subscription service on USIM1 with operator 1, while the user also has a personal subscription service for USIM2 with operator 2. The user wants to be able to receive voice calls and access data services from either service with a subscription on either USIM1 or USIM2 depending on the time of day or the application they are using the service for.

(assignment)
As can be seen from the above use cases, a multi-SIM UE utilizing common radio and baseband components needs to decide which SIM to serve at any given time. Current implementations of multi-SIM UEs are proprietary, and as a result, implementations may differ and UE behavior may differ. This difference in behavior may adversely affect core network operation, as many operations and algorithms are optimized based on the CN's knowledge of the UE's behavior. Both 3GPP SA1 and SA2 working groups are currently studying issues related to supporting UEs with multiple SIMs.

In those studies, it is proposed to standardize multi-SIM UEs and corresponding procedures to provide knowledge of the UE's behavior to the core network and enable optimal operation of the UE communicating to either network. This study focuses on UE implementations where common radio and baseband components are used to support multiple SIMs in the UE. Issues such as how the UE informs the CN of its multi-SIM capabilities, how the UE knows when to monitor paging opportunities associated with pages in either SIM, how the UE switches operation from one SIM to the other, how the UE informs the CN when switching SIM usage, how to minimize paging collisions, and what policies the UE uses to provide service type prioritization among multiple SIMs are yet to be determined. In addition, support for multiple SIM UEs is expected in both LTE and 5G systems.

One major problem with UEs operating with multiple SIMs and using common radio and baseband components is that of monitoring paging information by the UE of a second SIM when actively communicating with the first SIM. This is called paging collision, where paging opportunities associated with multiple SIMs overlap in time. A UE with a single transceiver needs to decide to monitor a single paging channel over other paging channels [6]. This decision can cause the UE to miss a page if it is not monitoring paging requests at the time of the inactive SIM's paging opportunity.

In several scenarios, paging collisions can occur in a multi-SIM UE. One scenario may be that when the UE is connected to the network of the active SIM, the UE is not actively monitoring the paging opportunities of the inactive SIM. Since the UE shares common baseband and radio components, the UE can only connect to one network at a time and monitor the paging opportunities associated with that network's SIM. If a page is sent for a SIM of another network, the UE cannot receive the page. This wastes radio resources at the RAN node that could be used for other purposes.

Another cause of paging collisions is when paging occasions of multiple SIMs overlap in time. Again, the UE can monitor and process paging occasions associated with one SIM with a single transceiver. When paging occasions overlap or are close together, the UE does not have enough time to switch connections to the other network. Again, this wastes radio resources at the RAN node.

Even if a multi-SIM UE is able to monitor paging opportunities associated with multiple SIMs, the constant switching performed to achieve this results in higher power consumption and shorter battery life for the UE. Furthermore, the UE may be switching to an unavailable connection for most of the time, and if there is no data for the UE, the UE may not be paged. A side effect of frequent switching is that the UE may be creating a scenario where paging collisions occur, and the UE may not be able to enter a DRX cycle to conserve battery power.

(overview)
Previous multiple SIM UEs were proprietary solutions implemented by device manufacturers without knowledge of the core network and are outside the scope of 3GPP standards. The behavior of the various entities (UE, RAN, and CN) was well defined and the operation of the cellular network was designed to be known among the various entities. In the various implementations of existing multiple SIM UEs, the various behaviors can adversely affect the operation of the network and even degrade its performance. As a result, the MUSIM study from the 3GPP SA1 and SA2 working groups is to define the architecture, interfaces, and procedures to support UEs with multiple SIMs.

The requirements described in the MUSIM study focus on UEs with common radio and baseband components shared by multiple SIMs installed in the UE, as well as dual Rx, single Tx UEs. The goal of the MUSIM work then is for a UE with multiple SIMs to provide the best possible service for each of the SIMs' operations. The central focus of the study is how a UE can provide seamless paging monitoring for multiple SIMs with common radio and baseband components. In this disclosure, a solution is proposed to address that problem, and also for the case of dual Rx, single Tx UEs. Specifically, the solution consists of the following:
Define enhancements to the UE registration and attach procedures to allow a multiple SIM UE to inform the core network that it is a multi-SIM device and to provide information about the other SIMs installed in the UE; Define new registration management states, sub-states or modes of operation for both the UE and the CN to maintain the UE's registration state per SIM; Define enhancements to the existing paging request mechanism to allow paging request forwarding from one PLMN to another to reach the UE; Define a SIM switching procedure by which the UE can indicate to the CN that it is switching to another SIM, while updating the UE's registration state in the CN and UE; Define an inactive registration timer update procedure that is performed through the active PLMN to maintain the registration timer of the inactive SIM; Define a procedure by which the UE can provide cell measurements taken for the inactive PLMN when attempting to establish a connection to the inactive PLMN after deciding to switch to it. Define a procedure by which the UE can request a new temporary identifier whose paging occasions are aligned or separated from those of another SIM. Define a procedure by which the UE can request the suspension of the registration timer, which will result in the CN also pausing paging for the UE. Define procedures by which the UE or CN may provide other information regarding the paging process. Define new policies in the 5G UE policies to allow the configuration of multiple SIMs, and give the user the ability to initiate a manual switch between SIMs through a GUI.

Concept 1:
The UE informs the CN that it is a multi-SIM device and provides the CN with information about the other SIMs.
- The UE sends a request to the first PLMN to register the second SIM in the second PLMN - The UE includes an indication and an identifier for the second SIM to be registered in the second PLMN - The first PLMN forwards the request to the second PLMN - The second PLMN authenticates the UE's SIM credentials and provides the UE with a temporary identifier to be used for paging requests to the second SIM - The UE and the second PLMN update the UE's registration state for the second SIM Supplementary Features of Concept 1:
The UE is registered in a first PLMN for a first SIM The request is either a partial registration/attach or an indirect registration/attach request The UE is registered in a first PLMN and is requesting registration in a second PLMN The indication is a multi-SIM indication The identifier of the second SIM can be one of the following: SUPI (e.g. IMSI), GUTI, 5G-S-TMSI, or SUCI The temporary identifier assigned to the second SIM can be 5G-GUTI, GUTI, 5G-TMSI, TMSI, or 5G-S-TMSI The first PLMN also includes an identifier of a network node supporting multi-SIM operation and an identifier of the first SIM authenticated in the first PLMN The registration state of the UE is RM-INACTIVE or EMM-INACTIVE after successful registration with the second PLMN. The first PLMN may assign a second temporary identifier for the second SIM and store the registration state of the UE for the second SIM. The UE provides multi-SIM support information to the CN, which may consist of one or more of paging criteria, restricted paging area, paging occasion separation, number of pages missed before notification, proposed temporary identifier.

Concept 2:
The first PLMN forwards the paging request to the UE through the second PLMN.
The first PLMN receives data associated with the first SIM The first PLMN forwards a paging request to the second PLMN, the paging request including the temporary ID associated with the first SIM The second PLMN sends a paging request to the UE on a paging occasion that the UE monitors The UE retrieves the paging information and receives the temporary identifier associated with the first SIM Supplementary features of concept 2:
- The UE supports multi-SIM operation - The UE has concurrent registrations with both the first and second PLMN - The UE has an inactive registration with the first PLMN - The UE has an active registration with the second PLMN - A paging request is sent in an encrypted NAS container from the first PLMN to the second PLMN - The paging occasion is calculated from a temporary identifier in SIM1 - The paging occasion is calculated from a temporary identifier in SIM2 - The paging information includes the service category of what the page is for, which may be classified as voice call, SMS message, or other data (e.g. application data), control plane signaling, emergency message, emergency callback, mobile terminated exception data, etc. - The paging information includes the PDU Session ID and Application ID associated with the page - The UE sends a response to the first PLMN through the second PLMN

Concept 3:
The UE performs a SIM switching procedure.
The UE receives paging information for data associated with the second SIM while connected to the first PLMN. The UE decides to switch to the second PLMN to retrieve the data based on the service type prioritization indicator provided in the paging information. The UE informs the first PLMN to suspend the registration status of the first SIM. The UE and the first PLMN update the registration status of the first SIM on the UE and the first PLMN. The UE attempts to establish communication with the second PLMN for the second SIM. Supplementary Features of Concept 3:
- The paging information provides a service type prioritization that may include a service category, PDU session ID, and application ID associated with the data for which the UE is paging - The UE checks the service type prioritization against its internal policies and finds a match - The UE sends a registration update request with registration type set to SIM switching - The first PLMN activates paging request forwarding for the first SIM - The registration state of the first SIM is set to RM-INACTIVE or EMM-INACTIVE in the UE and the first PLMN - The first PLMN sends a response to the second PLMN from which the UE received the paging request - Establishing communication with the second PLMN includes sending a registration update request including the SIM switching registration type

Concept 4:
The UE updates the registration timer of the second PLMN through the first PLMN.
- The UE sends a request to the first PLMN to update the registration timer of the second SIM on the second PLMN - The first PLMN forwards the request to the second PLMN - The second PLMN updates the registration timer for the second SIM in the second PLMN - The second PLMN returns a response to the first PLMN - The first PLMN forwards the response to the UE Supplementary features of concept 4:
- The request may be a registration update, a tracking area update, or an inactivity registration timer update - The request includes a temporary identifier associated with the second SIM - The response may include the status of the registration update request, the new value of the registration timer, or an updated TAI list - The response may include an indication that the registration status of the second SIM is no longer valid - The second PLMN may allocate a new temporary identifier for the second SIM and include it in the response to the UE

Concept 5:
The UE collects cell measurement information while attached to the second PLMN after the SIM switching procedure and provides measurements to the second PLMN directly upon attachment or through the first PLMN if the attachment is not successful.
The UE collects cell measurements while attempting to connect to a second PLMN after disconnecting from a first PLMN The UE provides the cell measurements to the RAN node after successful connection to the second PLMN The UE connects to the first PLMN after a failed attempt to connect to the second PLMN, including the collected measurements and cause code The first PLMN forwards the measurements and cause code to the second PLMN Supplementary features of Concept 5:
If the UE successfully connects to the second PLMN, the UE formats the cell measurements into a drive test minimization report to the RAN node of the second PLMN. The cell measurements indicate the signal strength of cells belonging to the second PLMN. The cell measurements include the location and time the measurements were made. The cell measurements may be queued by the UE and sent to the RAN node upon future successful connections. The UE stores the cell measurements and the cause code after a connection to the second PLMN fails. The cause code may be received from the second PLMN or generated by the UE. The cause code may indicate that the RAN node is overloaded and will not accept new registrations. The cause code may indicate that the mobility management node is overloaded and will not accept new registrations. The cause code may indicate that the signal strength of the cell is not strong enough to maintain a connection with the second PLMN. The cause code may indicate that there are no cells available to establish a connection with the second PLMN.

Concept 6:
The UE requests a new temporary identifier whose paging occasions are aligned or separated from paging occasions associated with another SIM.
- The UE is registered with a first PLMN and receives a temporary identifier with an associated paging occasion for a first SIM - The UE is registered with a second PLMN and receives a temporary identifier with an associated paging occasion for a second SIM - The UE determines that there is a possibility of a paging collision between the paging occasions of the two SIMs - The UE makes a request to obtain a new temporary identifier whose paging occasion is different from the previous paging occasion Supplementary features of concept 6:
- The request may be, for example, one of an initial registration, a mobile registration update, a periodic registration update, an attach, or a tracking area update request - The UE may provide parameters in the request to assist the network in allocating a new temporary identifier - The new parameters may be, for example, a paging criteria, a restricted paging area, a paging occasion separation, a multi-SIM indicator, a temporary identifier, or multiple paging occasions - The network may allocate a temporary identifier whose paging occasion is, for example, the same as, nearby, far away, or different from an existing paging occasion - The network may allocate multiple temporary identifiers to the UE corresponding to multiple paging occasions

Concept 7:
The UE requests to pause the registration timer associated to the SIM The UE registers with the PLMN and the PLMN starts the registration timer The UE sends a request to activate the registration pause timer The CN pauses the registration timer and starts the registration pause timer The CN provides a response that the registration pause timer is active Supplementary features of concept 7:
- The request may be for example one of the following: initial registration, mobile registration update, periodic registration update, attach or tracking area update request - The UE may provide an expiry value for the registration pause timer - The UE may request the CN to queue any downlink data for the UE while the registration pause timer is running - The CN maintains the context for the UE, e.g. registration state, security context, PDU sessions etc - The CN may return a new value for the expiry of the registration pause timer - The CN may provide an indication to queue downlink data for the UE

Concept 8:
The UE or the CN provides information about a problem with the paging process The UE has registrations for multiple SIMs The UE is receiving data on a first SIM The UE receives a page on a second SIM The UE or the CN informs the other of a problem with the paging process Supplementary features of concept 8:
- The notification may be a request sent by the UE - The request may be, for example, one of the following: Mobile Registration Update, Periodic Registration Update, Tracking Area Update, or Service Request - The UE may provide an instruction for the CN to stop paging the UE - The notification may be a response sent by the CN - The response may contain, for example, an instruction to inform the UE that it has missed a previously sent page, the time of that page, the tracking or registration area where the page was sent, and other information about the page such as service category, telephone number, PDU session ID, and application ID

Detailed Description As highlighted by the MUSIM study [6], current multi-SIM UE implementations with common radio and baseband components raise many issues related to different UE behaviors that can degrade network performance. To solve such problems, a more integrated solution is proposed in which the UE communicates support for multi-SIM functionality to the core network using a newly proposed registration request, and the network enhances the paging mechanism through providing service prioritization information in paging messages and enabling paging request forwarding to minimize UE switching cycles between SIMs. These enhancements allow the UE to receive page prioritization information for multiple SIMs by only monitoring the paging occasions calculated for the active SIM, rather than requiring the UE to switch operation to monitor paging opportunities for each SIM. In addition, the network is made aware of the UE's new registration state, sub-state, or mode of operation through the new SIM switching procedure and by enhancements to the UE registration state. This enhancement allows entities in the cellular system to have knowledge of the operation of the multi-SIM UE. The solution proposed here is designed based on the following assumptions:
1. UE implementations with multiple SIMs share common radio and baseband components, and several solutions are presented to address dual Rx, single Tx capable UEs. 2. The multiple SIMs are from the same or different PLMNs (PLMN refers to networks of different operators, also called Mobile Network Operators or MNOs). 3. Optionally, PLMNs have roaming agreements with each other and can support authentication of SIMs as proposed herein. 4. Security support for multi-SIM operation between the UE and the core network is established. 5. Both the UE and the core network support the multi-SIM functionality proposed herein.

However, there may be cases where there is no coordination between mobile network operators or MNOs. In these cases, an alternative solution is presented that does not require coordination between MNOs, where the UE can request a different temporary identifier from the network that corresponds to a different paging occasion than the currently assigned PO. This and other solutions are also presented to address the no MNO coordination scenario. It should be noted that certain aspects of the solutions associated with MNO coordination may also be used in the no MNO coordination scenario. For example, the core network assigning temporary identifiers that associate the same PO for multiple SIMs may be used in the no MNO coordination case. This may be utilized in the intra-MNO case where multiple SIMs belong to the same MNO.

A solution that supports multi-SIM UEs is necessary for both 5GS and LTE systems. Therefore, this disclosure applies the proposed solution to both 5GS and LTE systems. Where a solution is presented for only one system, the solution may easily be applied to the other system.

Figure 9 shows the main steps of the proposed solution for a UE with two SIMs, but the solution can be extended to a UE with three or more SIMs. The figure shows a UE registering in two PLMNs using different SIMs, SIM1 and SIM2. The UE has service subscriptions for both SIM1 and SIM2, communicates with PLMN1 primarily using SIM1, and simultaneously registers with PLMN2 for SIM2, requesting PLMN2 to forward paging requests for SIM2 to PLMN1 for further processing. Thus, the UE only needs to monitor paging occasions associated with SIM1 on PLMN1 to receive paging requests for both SIM1 and SIM2. Similarly, the UE can receive paging requests for both SIM1 and SIM2 when the UE is communicating with PLMN2 by only monitoring paging occasions associated with SIM2 on PLMN2. Note that the UE can receive pages for multiple SIMs, e.g., active SIMs as well as inactive SIMs, while only monitoring paging opportunities on the active PLMN. The inter-registration of SIMs between PLMNs and paging request forwarding features allow the UE to operate in this manner, thereby reducing the required power consumption, and still be able to receive pages for multiple SIMs.

Two different registration procedures are proposed in Fig. 9 to link SIM1 and SIM2 in their respective PLMNs: partial registration procedure and indirect registration procedure. These registration procedures allow all paging requests, whether for SIM1 or SIM2, to be received by the UE on the PLMN where the UE is actively registered. In other words, paging requests of inactive SIMs are received at paging opportunities of active SIMs. This solution solves the paging collision problem as mentioned above, since the UE can receive pages of multiple SIMs without having to frequently switch connections between different PLMNs.

The SIM switching procedure is utilized by the UE to inform the active PLMN to suspend the UE's registration state so that the UE can either establish communication with the inactive PLMN to complete processing of paging requests or use subscribed services associated with the inactive SIM. Using this procedure, the UE can switch between subscribed services offered by two SIMs and still receive paging requests for either SIM, regardless of which PLMN the UE is actively registered in at any given time. This procedure informs the core network of the UE's intention to switch connections between PLMNs, thereby solving the problem of the network not knowing what the UE is doing with multiple SIM applications.

Step S900: The UE registers with PLMN1 using SIM1 and establishes a PDU session on PLMN1. The UE can provide a multi-SIM indication to PLMN1 to inform PLMN1 that the UE is a multi-SIM device and provide a UE identifier (e.g., SUPI (e.g., IMSI), GUTI, 5G-S-TMSI, or SUCI) of SIM2 to be used in the partial registration procedure shown in step S902b. The inclusion of the multi-SIM indication and UE identifier(s) supports the case where two SIMs are installed before the UE performs the UE initial registration procedure. This step can be triggered by the insertion of a second SIM, download of a second SIM profile to the eSIM, an indication from a GUI, or through a power cycle event.
Step S909: Alternatively, the UE can separately inform PLMN1 that it is a multi-SIM device and provide the UE identifier of SIM2 to PLMN1 to initiate the partial registration procedure shown in step S902b. Note that steps S900 and S902a are different ways to initiate the partial registration procedure. For example, step S902a may be performed by the UE when the two SIMs are installed at different times. In step S902b, PLMN1 performs partial registration with PLMN2 for SIM2. The AMF of PLMN1 may contact either the AUSF and/or UDM of PLMN2 and provide the following information to link the two SIMs together: an indication that partial registration has been requested, an indication that the UE is a multi-SIM device, UE identifiers of SIM1 and SIM2, an indication that SIM1 has been authenticated and registered with PLMN1, multi-SIM support information, etc. PLMN2 may store this information in UDM2, while PLMN1 may store the same information in UDM1, plus information returned to the UE after successful registration (such as a temporary identifier). The UE identifier in this case may refer to both permanent and temporary identifiers used to associate with the SIMs. The multi-SIM support information may be provided to assist the network in enhancing the paging process for multi-SIM UEs.
Step S904: As an alternative to partial registration, the UE can perform an indirect registration of SIM2 with PLMN2 through PLMN1 in order to establish a registered state with PLMN2. This can be performed in either the control plane or the user plane. The outcome of the indirect registration, if successful, is similar to that of a general registration in TS 23.502 [2], i.e., the UE establishing a registered state with the core network as outlined in the assignment of temporary identifiers, network slices, update timers, DRX parameters, etc. However, certain enhancements as proposed below for multi-SIM operation apply to the indirect registration. This registration procedure can bring the UE into RM-INACTIVE state and provide the UE with a set of temporary identifiers different from those returned from the general registration procedure. The procedure can link SIM1 and SIM2 together on PLMN2, similar to the link established by partial registration to enable paging request forwarding. Like partial registration, indirect registration may be initiated as part of general registration or may be initiated stand-alone as a separate registration step (i.e., similar to steps S900 and S902a, but for indirect registration).
Step S906: After some time, the UE receives a paging request for SIM2 from PLMN1. The paging request originates from PLMN2, which forwards the request to PLMN1. Note that the detailed paging information may be sent from PLMN2 to PLMN1 in an encrypted NAS container to protect the privacy of the UE. The paging request is found in a paging occasion associated with SIM1, and when the UE reads the paging channel, the paging information is associated with SIM2. The paging information may include a service type prioritization of the page to enable the UE to make a decision whether to continue processing the paging request. In addition, the UE may obtain more detailed paging information by performing a service request procedure and receiving the encrypted NAS container with the service prioritization information. Alternatively, the forwarded paging request may be received by the UE as a NAS notification through the user plane of the network.
Step S910: The UE informs PLMN1 that it needs to perform a "SIM Switch" procedure towards PLMN2. Since PLMN1 is aware of SIM2 and has linked information for SIM2, PLMN1 assists the UE to perform SIM Switch. This procedure changes the UE's registration state on PLMN1 to RM-INACTIVE, which is a new registration state, sub-state, or operation mode of the RM-REGISTERED state proposed by this solution to indicate that the UE's registration to PLMN1 is temporarily suspended. The UE's context in PLMN1 is preserved for SIM1 to enable the UE to switch to using SIM2 on PLMN2. The preserved context allows the UE to quickly resume operation back to PLMN1. Other alternatives to the SIM switching procedure have also been proposed, where a multi-SIM UE can inform the network to suspend the registration state of one SIM, so that the UE can communicate with another SIM. During the suspension of the registration state, the paging mechanism can be changed, such as the network forwarding paging requests, filtering paging messages to the UE, buffering downlink data, etc.
Step S912: The UE performs a periodic registration update procedure to change the registration status of SIM2 from RM-INACTIVE to RM-REGISTERED. It should be noted that before performing a periodic registration update, the UE may need to first perform procedures including cell search, PLMN selection, establishment of an RRC connection with RAN2, etc. Upon receiving the registration acceptance response, the UE can then perform either a service request procedure or a PDU session establishment procedure to retrieve data associated with the paging request. The UE may perform a service request as an alternative to a periodic registration update.
Step S914: After the UE completes the session for retrieving the data associated with the paging request, the UE can suspend the registration state of SIM2 by performing a SIM switching procedure, as shown in step S1914a, and then reactivate the registration state of SIM1, as shown in step S1914b.

Another enhancement not shown in FIG. 9 is the Inactive Registration Timer Update procedure, where the UE can request an update of the registration timer of the inactive SIM through the active PLMN. This procedure provides the inactive PLMN with an update that the UE is still connected to the active PLMN and can therefore receive forwarded paging requests. Another enhancement allows the UE to collect cell measurement information while attempting to establish a connection with the PLMN after the SIM switching procedure. These measurements can be provided to the PLMN if the connection establishment is successful or through another PLMN if the connection is not successful. The cell measurements can be used by the network operator to determine the network coverage and improve the cellular coverage of the system if necessary. There are also other enhancements proposed for multi-SIM operation in MNOs without coordination.

When describing multi-SIM operation, it is important to define the terms for use that clearly distinguish which SIM/PLMN the UE is actively using to communicate at any given time. The terms "primary" and "secondary" refer to the SIM prioritization as outlined by the UE policy or by the user via a GUI. These terms indicate which SIM has priority (primary) over the UE's other SIMs (secondary). The UE typically uses the primary SIM most of the time. The terms "active" or "inactive" refer to the SIM/PLMN with which the UE is currently communicating. In other words, the UE maintains a connection to a PLMN that is "active" and has no connection to an "inactive" PLMN. The use of the terms is explained below using FIG. 9 as an example.
・Primary SIM = SIM1
・Secondary SIM = SIM2
Active SIM/PLMN = SIM1/PLMN1 (for steps 1-5), SIM2/PLMN2 (for steps 6-7)
Inactive SIM/PLMN = SIM2/PLMN2 (for steps 1-5), SIM1/PLMN1 (for steps 6-7)
The terms primary and secondary may also be applied to PLMNs when it is not initially known which PLMNs are active PLMNs and which are inactive PLMNs, e.g., before a UE registers with a PLMN.

The following solution applies when the SIMs are from different operators. However, the solution may also be adapted to support SIMs from the same operator. For example, the registration procedure applies to the same PLMN and does not depend on roaming agreements between PLMNs. The procedure still links the paging requests of SIM1 and SIM2 together and the UE receives the paging request on the paging occasion of the active SIM. The registration state transition and SIM switching procedure remain the same whether the SIMs are from the same or different operators. In the same operator case, the UE does not need to switch connections between PLMNs after performing the SIM switching procedure.

Note that although the following solutions are described within the context of 5GS, the solutions may also apply to EPS. For example, the proposed registration procedure may be performed in the MME in EPS, which functions similarly to the AMF in 5GS. Note that in 5GS, NAS messaging is between the UE and the AMF, and in EPS, NAS messaging is between the UE and the MME. In EPS, the attach procedure and the HSS perform functions similar to the general registration procedure and UDM in 5GS, respectively. The RAN nodes are eNodeBs for EPS and gNodeBs for 5GS. Similarly, the RM-INACTIVE state proposed herein for 5GS could be a new state such as EMM-INACTIVE in EPS. The SIM switching procedure may be performed in both EPS and 5GS as well, and multi-SIM policies or information elements may be incorporated in both systems. The solution in this disclosure describes how policies can be delivered to the UE from the PCF via NAS messaging. In EPS, policies can be delivered to the UE via IP-based procedures from the ANDSF server or via information elements sent in NAS messages. Embodiments are provided to illustrate some of these enhancements as they apply to an EPS system.

Different aspects of the LTE system are enhanced to support the use of multi-SIM UEs. The first aspect applies to the attach procedure that the UE performs to register with the core network. These enhancements to the attach procedure are proposed: partial attach, indirect attach, and MUSIM attach. These attach procedure enhancements include the registration of the multi-SIM used in the UE. Partial attach registers the secondary SIM with the HSS of the corresponding PLMN which triggers a paging request forwarding originating from the HSS. On the other hand, indirect attach registers the secondary SIM with the MME of the corresponding PLMN and can establish a default bearer for PDN connectivity at all times. Finally, the MUSIM attach enhancement allows the UE to indicate to the core network with a single request the need to perform an attachment procedure for multiple SIMs, which can trigger the execution of either a partial or indirect attachment procedure for the secondary SIM.

In addition, a new LTE EMM state is proposed to be added to the UE and MME to support a new registration mode of operation enabled for multiple SIM UEs, namely EMM-INACTIVE. This new registration state indicates that a UE operating with a secondary SIM is registered with the corresponding PLMN but is not actively connected with that PLMN. Furthermore, the aforementioned attachment procedure enhancement enables paging request forwarding. Paging request forwarding refers to the process whereby a paging request for an inactive SIM is forwarded by an inactive PLMN to an active PLMN in order to page the UE. All these LTE system enhancements are similar to 5G enhancements and are described in more detail below.

Note that although this disclosure refers to EMM-INACTIVE as a new state in the EMM state model, for current LTE deployments it may be more feasible that it could instead be a sub-state or mode of operation within the EMM-REGISTERED state. This sub-state or mode of operation is sometimes referred to as an "inactive registration" sub-state or mode of EMM-REGISTERED. Also note that the UE and MME can maintain separate EMM and ECM states for each SIM.

Once the registration state is established for each of the SIMs of a multi-SIM UE, the functionality of paging request forwarding is enabled to eliminate the occurrence of paging collisions. When data is available for an inactive SIM, the corresponding PLMN forwards the paging request to the UE through the active PLMN. Within the active PLMN, the calculation of paging occasions is such that the UE can receive paging requests for multiple SIMs, while it only needs to monitor one paging occasion. Paging information may possibly be transmitted via NAS notification, as described below.

(Multiple SIM Registration Procedure)
An E-UTRAN cell may broadcast in its system information broadcast whether a UE can connect to an MME that supports partial and/or indirect attach. The UE may check that the E-UTRAN cell is broadcasting this indication before attempting to perform a partial and/or indirect attach with the network via the E-UTRAN cell.

Note: This same checking operation can be performed in 5G systems. In other words, an NR cell can broadcast in its system information broadcast whether it can connect to an AMF that supports partial and/or indirect attach. The UE can check that the NR cell is broadcasting this indication before attempting to perform a partial and/or indirect attach with the network via the NR cell.

As mentioned before, in this disclosure, two registration procedures are proposed to support multi-SIM operation in 5GS. The registration procedure allows the UE to receive services from the 5G network. The partial registration is invoked by the UE to register the SIM in the secondary PLMN via the primary PLMN. By performing this registration, the UE is informing the secondary PLMN to forward all paging requests to the UE through the primary PLMN when the UE is not actively registered in the secondary PLMN. On the other hand, the indirect registration performs a full registration with the secondary PLMN through the primary PLMN as outlined in the general registration procedure found in TS 23.502 [2]. The indirect registration procedure also informs the secondary PLMN to forward all paging requests to the primary PLMN when the UE is not actively communicating with the secondary PLMN. In both registration procedures, the RM state of the UE with the secondary PLMN transitions from RM-DEREGISTERED to RM-INACTIVE. In the case of indirect registration, an AMF is assigned to serve the UE, which differs from partial registration in that no AMF is assigned to serve the UE.

Similar to the 5G registration procedure, the UE needs to perform an attach procedure with the core network of the LTE system to be able to receive services from the network. The attach procedure registers the UE to the core network by authenticating the UE and establishing a context for the UE to communicate securely with the network. In the multi-SIM case, it is proposed that the attach procedure is enhanced to support the registration of multiple SIMs. In this specification, enhancements are described for 1) partial attachment, 2) indirect attachment, and 3) MUSIM attach. MUSIM attach combines multiple attach requests into a single request, e.g., an attach request for the primary SIM and one or more attach requests for the secondary SIMs. The MUSIM attach procedure can be applied to the 5G system as well.

For all described registration and attach procedures, the UE may include multi-SIM support information in the corresponding request message, such as information configured in the UE (e.g., by the user). The support information may be used by the network to enhance existing paging mechanisms for multi-SIM operation. For example, the support information may provide prioritization information informing whether and when to page the UE when downlink data is available for a particular SIM. Furthermore, the support information may provide information on how the network can assign identifiers corresponding to paging occasions so as to avoid paging collisions for multiple SIMs. Multi-SIM support information is described in more detail below.

(Partial registration)
The UE performs partial registration primarily to configure the secondary PLMN to forward all paging requests to the UE through the primary PLMN whenever the UE's RM state with the secondary PLMN is RM-INACTIVE. This procedure allows the UE to receive all paging requests, whether the paging request is for SIM1 or SIM2, on paging occasions associated with the active SIM, regardless of the PLMN with which the UE is actively communicating. As a result, the UE does not need to switch network connections between SIMs to receive paging requests. In fact, this procedure ensures that the UE receives all paging requests, but the procedure for switching the UE between SIMs may miss paging requests if the switching timing is not aligned with the timing of the paging requests. It is noted that the partial registration enhancement allows the page request forwarding functionality to originate from the UDM, which is a new functionality added to the UDM.

Figure 10 shows a UE initiating a partial registration procedure for SIM2 through PLMN1. The figure shows two cases in which partial registration of SIM2 can be done, namely 1. when both SIMs are installed together and the partial registration request is part of the initial registration request (this is called MUSIM registration) or 2. when SIM2 is installed after SIM1 is installed and the UE has already performed the initial registration of SIM1.

Step S1002: The UE registers in PLMN1 in SIM1 with a registration type of initial registration. At this time, only SIM1 is installed in the UE. However, if both SIM1 and SIM2 are installed at the same time, the UE may include a multi-SIM indication with an appropriate SIM2 identifier (e.g., SUPI (e.g., IMSI), GUTI, 5G-S-TMSI, or SUCI) when the UE registers in PLMN1 in SIM1. In this case, it is proposed that the partial registration request is integrated as part of the general registration procedure (general registration procedure described in TS 23.502 [2]) performed for SIM1. This procedure may be referred to as MUSIM registration. The addition to the initial registration request is to include the multi-SIM indication, partial registration indicator, and one or more SIM2 identifiers, as described above. The multi-SIM indicator may be coded as an option in the preferred network behavior parameter or may be a standalone indicator, and the partial registration indicator may be embedded within the registration type parameter. The message may further indicate which SIM is the primary SIM and which is the secondary SIM and should be used to register with the inactive PLMN. In this case, processing skips to step S1006.
Step S1004: After the UE successfully registers SIM1 to PLMN1 and SIM2 is installed in the UE, a partial registration request may be initiated by the UE to inform PLMN1 that the UE is a multi-SIM device and includes a multi-SIM indication and a SIM2 identifier, if applicable. The registration type of this request may be partial registration or a partial registration indicator may be provided. At this point, the RM state of SIM1 is RM-REGISTERED and for SIM2 (with PLMN2) is RM-DEREGISTERED. The SIM2 identifier is used by PLMN2 to authenticate SIM2 to the UE and may consist of SUPI (e.g., IMSI), GUTI, 5G-S-TMSI, or SUCI. The partial registration request may be a newly defined procedure or may be incorporated as part of the general registration procedure. The multi-SIM indicator may be coded as an option in the preferred network behavior parameters or may be a standalone indicator that may be used by the network entity to check and select an appropriate network entity that supports multi-SIM operation during the registration procedure.
Step S1006: RAN1 forwards the partial registration request to AMF1 via the N2 interface previously established for SIM1. In case of MUSIM registration, RAN1 selects AMF1 to process the request.
Step S1008: Due to the presence of the multi-SIM indication and/or the fact that the UE 102 is requesting partial registration, the AMF1 904 selects and requests the AUSF2 908 to authenticate the UE 102 for SIM2 by sending the SIM2 identifier with the multi-SIM indication and partial registration indicator to the AUSF2 908. If the request was for MUSIM registration, the AMF1 904 may first register SIM1 and then send the partial registration request for SIM2. It is to be noted that it is assumed that there is a roaming agreement between PLMN1 and PLMN2, and the AMF in each PLMN may be configured with the contact information of the AUSF of the other PLMN to forward the partial registration request. It is also envisaged that communication between AMF1 904 and AUSF2 908 is ensured via the N32 interface, for example through the SEPPS of the corresponding PLMN.
Step S1010: AMF1 904 forwards a partial registration request to AUSF2 908, with the registration type set to partial registration, or with a partial registration indicator, the multi-SIM indication may be coded as an option of preferred network behavior, and may include the SIM2 identifier, the AMF1 ID and UE ID indicating that the UE with SIM1 is authenticated to PLMN1, the context information of the AMF of PLMN1 to which PLMN2 can forward future paging requests for SIM2, etc. It should be noted that in step S1002, the registration type was set to initial registration for SIM1, but this registration request is targeted to SIM2, and therefore the change of registration type from initial registration to partial registration for this request is to AUSF2 908. Alternatively, the registration type may be set as initial registration and a partial registration indicator may be provided in the request. The registration type in step S1002 may be coded as initial registration with partial registration.
Step S1012: The AUSF2 908 may perform authentication of the UE for SIM2 and create or update subscription information in the UDM2 910. The UDM2 910 may provision the UE 102 with a temporary identifier for SIM2 that is used to indicate when a paging request is targeted to SIM2. In addition, the RM status of SIM2 is updated to RM-INACTIVE to enable forwarding of paging requests to the UE through PLMN1. The RM status in this case may be an indication stored in the subscription data of the UDM to indicate that paging request forwarding is enabled.
Step S1014: After the AUSF2 authenticates the UE for SIM2, a partial registration accept message is returned to the AMF1. The partial registration accept message may be a modified registration accept message. The AUSF2 may include the following information in the accept message: an indication that the authentication of SIM2 was successful, a temporary identifier assigned to the UE for SIM2 by the UDM2, an indication that the UE's RM state for SIM2 has changed from RM-DEREGISTERED to RM-INACTIVE, an acknowledgement of support for receiving paging requests forwarded by PLMN1 for SIM1, contact information of the MME for receiving paging requests from PLMN1, and a registration timer for SIM2. The temporary identifier for the UE is used to page the UE whenever there is a page for SIM2 while the UE is actively registered in PLMN1. In addition, contact information of the default AMF may be included in the acceptance message to inform AMF1 that future paging requests may originate from the default AMF rather than the UDM.
Step S1016: AMF1 forwards a partial registration accept message to the UE through RAN1, including the information returned from AUSF2 to AMF1. The accept message may include an indication of successful authentication of SIM2, a temporary identifier assigned to the UE for SIM2 by UDM2, an indication that the UE's RM state for SIM2 has changed from RM-DEREGISTERED to RM-INACTIVE, and a registration timer for SIM2. The temporary identifier for the UE is used to page the UE from PLMN2 using the paging request forwarding function whenever there is a page for SIM2 while the UE is actively registered in PLMN1. Alternatively, AMF1 may assign a separate temporary identifier for SIM2 that may be used to page the UE in PLMN1 instead. The allocation of this temporary identifier may be such that the associated paging occasion occurs overlapping with the paging occasion associated with SIM1. Thus, the UE only needs to monitor one paging occasion to receive pages of both SIM1 and SIM2. AMF1 may alternatively assign the same temporary identifier to all SIMs associated with the UE while maintaining the fact that the UE only needs to monitor one paging occasion and can receive pages of all SIMs. The UE's RM state for each SIM is updated in the UE and should match that of AMF1, i.e. RM-REGISTERED for SIM1 and RM-INACTIVE for SIM2.

This procedure proposes that the UDM assigns a temporary identifier to the UE, and that the temporary identifier is provided to the UE. This temporary identifier may be a new type of 5G-GUTI. This 5G-GUTI may be formatted in a way that is compatible with the existing 5G-GUTI format. For example,

The GUAMI may contain only <MCC> and <MNC> so that it can be resolved to the UDM/UDR. The fact that the GUAMI does not contain <AMF Region ID>, <AMF Set ID> and <AMF Pointer> may indicate that the 5G-GUTI was assigned by the UDM.

The 5G-TMSI of the 5G-GUTI may be a temporary identifier assigned to the UE by the UDM, or it may be the SUCI or GPSI. This temporary identifier may be included in the paging message so that the UE can detect that it is being paged to the associated SIM.

(Partial registration alternative method)
This section proposes an alternative procedure for the UE to perform partial registration, which is shown in FIG.

Step S1102: The UE registers in PLMN1 in SIM1 with a registration type of initial registration. At this time, only SIM1 is installed in the UE. However, if both SIM1 and SIM2 are installed at the same time, the UE may include a multi-SIM indication, a partial registration indicator, and an appropriate SIM2 identifier (e.g., SUPI (e.g., IMSI), GUTI, 5G-S-TMSI, or SUCI) when the UE registers in PLMN1 in SIM1. In this case, it is proposed that the partial registration request is integrated as part of the general registration procedure (general registration procedure described in TS 23.502 [2]) performed for SIM1. This procedure may be referred to as MUSIM registration. The addition to the initial registration request is to include the multi-SIM indication, partial registration indicator, and one or more SIM2 identifiers, as described above. The multi-SIM indicator may be coded as an option in the preferred network behavior parameter or may be a standalone indicator, and the partial registration indicator may be embedded within the registration type parameter. The message may further indicate which SIM is the primary SIM and which is the secondary SIM and should be used to register with the inactive PLMN. In this case, processing skips to step S1106.
Step S1104: After the UE successfully registers SIM1 to PLMN1 and SIM2 is installed in the UE, a partial registration request may be initiated by the UE to inform PLMN1 that the UE is a multi-SIM device and includes a multi-SIM indication and a SIM2 identifier, if applicable. The registration type of this request may be partial registration or a partial registration indicator may be provided. At this point, the RM state of SIM1 is RM-REGISTERED and for SIM2 (with PLMN2) is RM-DEREGISTERED. The SIM2 identifier is used by PLMN2 to authenticate SIM2 to the UE and may consist of SUPI (e.g., IMSI), GUTI, 5G-S-TMSI, or SUCI. The partial registration request may be a newly defined procedure or may be incorporated as part of the general registration procedure. The multi-SIM indicator may be coded as an option in the preferred network behavior parameters or may be a standalone indicator that may be used by the network entity to check and select an appropriate network entity that supports multi-SIM operation during the registration procedure.
Step S1106: RAN1 forwards the partial registration request to AMF1 via the previously established N2 interface for SIM1. In case of MUSIM registration, RAN1 selects AMF1 to process the request.
Step S1108: The AMF1 determines which UDM to connect to by examining the SIM2 identifier, which may include the MCC and MNC, which are used to determine the UDM to be contacted.
Step S1110: AMF1 forwards a partial registration request to UDM2, with the registration type set to partial registration, or a partial registration indicator, a multi-SIM indication may be coded as an option of preferred network behavior, and may include a SIM2 identifier, an AMF1 ID and a UE ID indicating that the UE with SIM1 is authenticated to PLMN1, context information of the AMF of PLMN1 to which PLMN2 may forward future paging requests for SIM2, etc. It should be noted that in step S1102, the registration type was set to initial registration for SIM1, but this registration request is targeted to SIM2 and thus is a change in the registration type from initial registration to partial registration. Alternatively, the registration type may be set as initial registration and a partial registration indicator may be added to the request. The registration type from step S1102 may be coded as initial registration with partial registration.
Step S1112: UDM2 responds to AMF1, and AMF1 responds to the UE. The response indicates to the UE whether the UE is allowed to be partially registered and indicates to the UE that authentication is pending. The message also includes a timer that indicates to the UE how long it should wait to receive a request from the network to initiate authentication. If the timer expires before the UE receives a request to initiate authentication from the network, the UE ignores the request to perform authentication unless it sends another partial registration request. UDM2 may provision the UE with a temporary identifier for SIM2 that is used to indicate when a paging request is targeted to SIM2. In addition, contact information of the default AMF may be included in the acceptance message to inform AMF1 that future paging requests may originate from the default AMF rather than the UDM. The RM state of SIM2 may not be updated or may be updated to a state indicating that authentication is pending.
Step S1114: The AMF initiates slice-specific secondary authentication with the UE and the AUSF of PLMN2. This procedure is described above in the section entitled "Slice-specific authentication and authorization". The UDM2 may provide the functionality of AAA-S 802 in the procedure. The UDM2 may provide a temporary identifier to the UE by providing the temporary identifier to the AMF. The AMF may provide the temporary identifier to the UE in an EAP success message. It may also provide a registration timer for SIM2. Figure 8 also shows AAA-P 804.

In partial registration, no AMF is assigned to serve the UE, and as a result, the UDM assigns a temporary UE ID to the UE. This temporary UE ID is used to page the UE whenever there is UE activity and the UE is in RM-INACTIVE state with the corresponding, inactive PLMN. Note that the RM state in this case may be an indication stored in the UDM subscription data to indicate that paging request forwarding is enabled. In this case, the UDM of the inactive PLMN may send a paging message to the AMF of the active PLMN with the temporary UE ID assigned to the UE during partial registration. In addition, the UDM may return the identifier and/or contact information of the default AMF in response to the partial registration request. This default AMF may be utilized to send paging requests for SIMs in which the UE is in RM-INACTIVE state with the PLMN to the AMF of the active PLMN where the UE is currently registered.

(Partial Attachment)
A multi-SIM UE can use the partial attach enhancement to register not only the primary SIM in the current PLMN, but also other secondary SIMs in their corresponding PLMNs. Figure 24 shows the partial attach enhancement procedure. Although this figure shows that the partial attach is performed separately from the initial attach of SIM1, they may also be combined together as one attach procedure, for example, in a MUSIM attach request, as described below. In addition, the partial attach enhancement can support partially attaching multiple secondary SIMs by performing steps S2406 to S2414 for each SIM. It should be noted that the partial attach enhancement allows the page request forwarding function to originate from the HSS, which is a new function added to the HSS.

Step S2402: The UE initially attaches to PLMN1 using SIM1. PLMN1 is considered as the active PLMN and SIM1 is considered as the primary SIM. This step may be initially performed when only SIM1 is installed in the UE. If two or more SIMs are installed in the UE at the same time, a combined attach procedure may be performed to register multiple SIMs together in one attach request. This combined attach request is called MUSIM attach and may include a multi-SIM indicator, a partial attach indicator, and appropriate SIM identifiers (e.g., IMSI, GUTI, etc.) for each SIM in addition to the information of a normal attach request. In this case, the partial attach is integrated as part of the attach procedure from TS 23.401 [9]. The multi-SIM indicator may be coded as an option in the preferred network behavior parameter or may be a standalone indicator, and the partial attach indicator may be carried in the attach type parameter. The message may further indicate which SIM is the primary SIM and which is the secondary SIM and should be used to register with the inactive PLMN. In case of a combined attach request, the procedure skips to step S2406.
Step S2404: After some time, a partial attach procedure is initiated. For example, this can be done when SIM2 is added to the UE by inserting a physical SIM, through eSIM configuration, based on a request from an application on the UE through a GUI or API, or immediately after completion of the attach procedure by PLMN1. SIM2 is considered a secondary SIM and associated with PLMN2. PLMN2 is considered an inactive PLMN. The UE then performs a partial attach request to PLMN2 through PLMN1. This request can include a multi-SIM indicator and an appropriate SIM identifier (e.g., IMSI, GUTI, etc.) for each SIM. The multi-SIM indicator may be coded as an option of the preferred network behavior parameter or may be a standalone indicator. The multi-SIM indicator can be used by the network entity to check and select an appropriate network entity that supports multi-SIM operation during the attach procedure and to enable paging request forwarding.
Step S2406: In response to the partial attach request or partial attach indication, the MME of PLMN1 selects an appropriate HSS to process the partial attach request for the respective SIM. The identifiers provided to SIM2 may include MCC and MNC, or may be resolved to MCC and MNC used to determine the HSS to be contacted. The MME of PLMN1 may be provisioned with contact information of other HSSs of different PLMNs due to core network configuration, roaming agreements, or other mechanisms supporting multi-SIM operation, so that the MME can forward any partial attach messages of those secondary SIMs to the default HSS of the other PLMNs.
Step S2408: MME1 2402 sends a partial attach request to the selected HSS. The request may include a partial attach indicator, a multi-SIM indicator that may be coded as an option for preferred network operation, a SIM2 identifier, an MME1 ID and a UE ID to indicate that the UE with SIM1 is authenticated to PLMN1, etc. MME1 may further provide context information of an MME in PLMN1 to which PLMN2 can forward the paging request for SIM2. This MME in PLMN1 may be configured to support paging request forwarding and may be able to forward the paging request from PLMN2 to an appropriate network entity (e.g., the MME to which the UE is attached in case of UE mobility) so that the UE receives the page.
Step S2410: The HSS of PLMN2 may perform authentication of the UE for SIM2 and store context information about the UE, such as information obtained from the authentication procedure as well as information provided by MME1. HSS2 2404 may also assign a temporary identifier to the UE for SIM2, which may be used by HSS2 to identify future forwarded paging requests of SIM2 to the UE through PLMN1. Finally, the EMM state of SIM2 is set to EMM-INACTIVE in HSS2 to indicate that the UE with SIM2 is registered in PLMN2 but is not actively communicating with PLMN2. The EMM state in this case may be an indication stored in the subscription data of the HSS to indicate that paging request forwarding is enabled.
Step S2412: The HSS of PLMN2 returns a partial attach accept response to the MME of PLMN1 indicating the result of the partial attach procedure. The response may include an indication that authentication of SIM2 was successful, a temporary identifier assigned by HSS2 for SIM2, an indication that the UE's EMM state for SIM2 has changed from EMM-DEREGISTERED to EMM-INACTIVE, an acknowledgement of support for receiving paging requests forwarded by PLMN1 for SIM1, contact information of the MME for receiving paging requests from PLMN1, and a registration timer for SIM2. If the partial attach was not accepted, the response may include further information detailing why the attach was not accepted. In addition, contact information of the default MME may be included in the accept message to inform MME1 that future paging requests may originate from the default MME rather than the HSS.
Step S2414: The MME of PLMN1 returns a partial attach accept message to the UE, which may be a modified attach accept message providing additional information regarding the status of the partial attach procedure. If the attach procedure was performed for multiple SIMs, there may be a separate registration status for each SIM. The response message may include information returned from the HSS of PLMN2, such as an indication that authentication of SIM2 was successful, a temporary identifier assigned to SIM2, an indication that the UE's EMM state for SIM2 has changed from EMM-DEREGISTERED to EMM-INACTIVE, and a registration timer for SIM2. The temporary identifier is used to identify future paging requests for SIM2 that are forwarded to PLMN1. In addition, the MME of PLMN1 may assign a separate temporary identifier for SIM2 that may be used to page the UE instead of using the temporary identifier assigned by PLMN2. The assignment of this temporary identifier may be such that the associated paging occasion overlaps with the paging occasion associated with SIM1. As a result, the UE only needs to monitor one paging occasion to receive pages for both SIM1 and SIM2. The MME may alternatively assign the same temporary identifier to all SIMs associated with the UE while maintaining the fact that the UE only needs to monitor one paging occasion and can receive pages for all SIMs. The UE's EMM state for each SIM is updated. In this scenario, the EMM state for SIM1 is EMM-REGISTERED and for SIM2 is EMM-INACTIVE. Similarly, the EMM state in the MME of PLMN1 is EMM-REGISTERED for SIM1 and EMM-INACTIVE for SIM2. The MME of PLMN1 may maintain separate EMM states for SIM1 and SIM2, respectively.

(Indirect registration)
The indirect registration procedure is a functional combination of the partial registration procedure and the general registration procedure. Both the partial registration procedure and the indirect registration procedure include a multi-SIM indication and a SIM2 identifier to configure PLMN2 to forward paging requests to the UE through PLMN1. However, the indicators for each procedure are different (i.e., indirect as opposed to partial), and the indirect registration procedure provides additional capabilities of the PLMN to allocate network slices and provide UE policy information to the UE. Indirect registration also allocates an AMF to serve the UE.

Figure 12 shows a UE initiating an indirect registration procedure for SIM2 through PLMN1. Note that, similar to the partial registration procedure, the indirect registration procedure may be combined with the general registration procedure to register both SIM1 (direct registration) and SIM2 (indirect registration) together in one request. This procedure may be referred to as MUSIM registration, as described below. Similarly, the indirect registration procedure may be performed separately from the general registration procedure.

Step S1202: The UE registers in PLMN1 of SIM1 with a registration type of initial registration. At this time, only SIM1 is installed in the UE. However, if both SIM1 and SIM2 are installed at the same time, the UE may also include a multi-SIM indication, an indirect registration indicator, an appropriate SIM2 identifier (e.g., SUPI (e.g., IMSI), GUTI, 5G-S-TMSI, or SUCI), and an identification information of PLMN2 when the UE registers in PLMN1 of SIM1. In this case, the indirect registration request of SIM2 is a part of the general registration procedure of SIM1, e.g., MUSIM registration. The addition to the initial registration request is to include the multi-SIM indication, the indirect registration indicator, the SIM2 identifier, and the identification information of PLMN2. The multi-SIM indicator may be coded as an option of the preferred network behavior parameter or may be a standalone indicator, and the indirect registration indicator may be incorporated within the registration type parameter. The message may further indicate which SIM is the primary SIM and which is the secondary SIM and should be used to register in the inactive PLMN, in which case the procedure skips to step S1206 and both the general registration of SIM1 and the indirect registration of SIM2 are performed simultaneously or may be performed sequentially, e.g., registration of SIM1 followed by registration of SIM2.
Step S1204: After the UE successfully registers SIM1 to PLMN1 and SIM2 is installed in the UE, an indirect registration request may be initiated by the UE to inform PLMN1 that the UE is a multi-SIM device and includes a multi-SIM indication, a SIM2 identifier, and an identification information of PLMN2. The registration type of this request may be indirect registration, or an indirect registration indicator may be provided. At this point, the RM state of SIM1 is RM-REGISTERED and for SIM2 (with PLMN2) it is RM-DEREGISTERED. The SIM2 identifier is used by PLMN2 to authenticate SIM2 to the UE and may consist of SUPI (e.g., IMSI), GUTI, 5G-S-TMSI, or SUCI. The indirect registration request may be a newly defined procedure or may be incorporated as part of the general registration procedure with registration type set as indirect registration or with the indirect registration indicator included. The multi-SIM indicator may be coded as an option in the preferred network behavior parameter or may be a standalone indicator. The multi-SIM indicator may be used by the network entity to check and select an appropriate network entity that supports multi-SIM operation during the registration procedure.
Step S1206: RAN1 902 forwards the general or indirect registration request to AMF1 904 via the previously established N2 interface for SIM1. In case of MUSIM registration, RAN1 902 selects AMF1 904 to process the request.
Step S1208: AMF1 904 performs steps S1008 to S1014 of Fig. 10 or 11 to authenticate the UE of SIM2. This step completes the UE's partial registration procedure for SIM2 and enables PLMN2 to forward paging requests originating from UDM2 to the UE. In addition, contact information of the default AMF may be included in the acceptance message to inform AMF1 that future paging requests may originate from the default AMF rather than the UDM.
Step S1210a and b: AMF1 requests slice selection subscription data of the UE from UDM2, and UDM2 responds with slice selection data to AMF1.
Step S1212a and b: AMF1 performs an Nnssf_NSSelection_Get request to NSSF2 1204 through NSSF1 1202 using the slice selection data retrieved from steps S1210a and b. AMF1 provides the requested NSSAI and other slice related parameters to NSSF2. NSSF2 returns a response including the allowed NSSAI and other NSSAI related parameters, as well as the NRF 302 for AMF1 to select the NF/service of the network slice instance.
Step S1214a and b: AMF1 queries NRF2 1208 through NRF1 1206 to find a suitable AMF to service the UE's indirect registration request. NRF2 returns a list of potential AMFs in PLMN2 to process the indirect registration request.
Step S1216: AMF1 forwards the indirect registration request to AMF2, which performs a general registration procedure of the UE using SIM2. The general registration procedure may also include a multi-SIM indication, an indirect registration indicator, and the appropriate SIM2 identifier or temporary identifier received in step S1208. AMF1 may obtain contact information of AMF2 through a network configuration supporting multi-SIM operation (e.g., through a roaming agreement) through NRF2 from step S1214 or through UDM2 from step S1208. Upon completion of the general registration procedure, the registration accept message returned to AMF1 may include an indication that authentication of SIM2 was successful, a temporary identifier assigned to the UE for SIM2 by AMF2, an indication that the UE's RM state for SIM2 has changed from RM-DEREGISTERED to RM-INACTIVE, an acknowledgement of support for receiving paging requests forwarded by PLMN1 for SIM1, contact information of the MME for receiving paging requests from PLMN1, and a registration timer for SIM2. The temporary identifier for the UE is used to page the UE from PLMN2 whenever there is a page for SIM2 while the UE is actively registered in PLMN1. Alternatively, AMF1 may assign a separate temporary identifier for SIM2 that may instead be used to page the UE in PLMN1. The allocation of this temporary identifier may be such that the associated paging occasion overlaps with the paging occasion associated with SIM1. Thus, the UE only needs to monitor one paging occasion to receive pages for both SIM1 and SIM2. AMF1 may alternatively assign the same temporary identifier to all SIMs associated with the UE while maintaining the fact that the UE only needs to monitor one paging occasion and can receive pages for all SIMs. The UE's RM state for each SIM is updated in the UE and should match that of AMF1, i.e. RM-REGISTERED for SIM1 and RM-INACTIVE for SIM2.
Step S1218: AMF1 returns the registration accept message received from AMF2 to RAN1, and RAN1 forwards the registration accept message to the UE. The accept message may include an indication of successful authentication of SIM2, a temporary identifier assigned to the UE for SIM2 by the general registration procedure or AMF1, an indication that the UE's RM state for SIM2 has changed from RM-DEREGISTERED to RM-INACTIVE, and a registration timer for SIM2. The temporary identifier for the UE is used to page the UE whenever there is a page for SIM2 while the UE is actively registered in PLMN1.

An alternative procedure for indirect registration is shown in Figure 13, where AMF1 is provisioned with the contact information of AMF2 as part of supporting multi-SIM operation. AMF2 is configured as the default AMF in PLMN2 for AMF1 to contact in case of multi-SIM support. On receiving the indirect registration request, AMF1 can search the contact list of PLMN2 and forward the indirect registration request directly to AMF2. AMF2 can select another AMF in PLMN2 to serve the UE based on the request forwarded from AMF1. From that point on, the general registration procedure from TS 23.502 [2] is performed, but with updates due to the changes to support indirect registration.

Steps S1302 to S1306: These steps are the same as those performed for the procedure shown in FIG.
Step S1308: AMF1 is provisioned with the contact information of AMF2 and sends an indirect registration of the UE for SIM2 to PLMN2. AMF1 makes this decision based on the presence of a multi-SIM indication or whether the registration type or indicator is set to indirect registration. The indirect registration request may include the registration type set to indirect registration or the indirect registration indicator, the multi-SIM indication may be encoded as an option of preferred network behavior, the SIM2 identifier, the AMF1 ID and UE ID indicating that the UE with SIM1 is authenticated to PLMN1, the context information of the AMF of PLMN1 to which PLMN2 can forward future paging requests for SIM2, etc. If the request of step S1302 was a general registration request, AMF1 generates a new indirect registration request where the registration type may be set to indirect registration and provides both the multi-SIM indication and the SIM2 identifier. Alternatively, the registration type may be set as initial registration and an indirect registration indicator may be added to the request. The registration type may be coded as initial registration with partial registration.
Step S1310: The general registration procedure from TS 23.502 [2] is performed towards SIM2 on PLMN2, but modified to include functionality to support indirect registration as outlined in FIG. 12.
Step S1312: AMF1 returns the registration accept message received from AMF2 to RAN1, and RAN1 forwards the registration accept message to the UE. The accept message may include an indication that authentication of SIM2 was successful, a temporary identifier assigned to the UE for SIM2 by the general registration procedure, an indication that the UE's RM state for SIM2 has changed from RM-DEREGISTERED to RM-INACTIVE, an acknowledgement of support for receiving paging requests forwarded by PLMN1 for SIM1, contact information of an MME for receiving paging requests from PLMN1, and a registration timer for SIM2. The temporary identifier for the UE is used to page the UE from PLMN2 whenever there is a page for SIM2 while the UE is actively registered in PLMN1. Alternatively, AMF1 may allocate a separate temporary identifier for SIM2 that may be used to page the UE in PLMN1 instead. This temporary identifier allocation may be such that the associated paging occasion overlaps with the paging occasion associated to SIM1. Thus, the UE only needs to monitor one paging occasion to receive pages for both SIM1 and SIM2. AMF1 may alternatively allocate the same temporary identifier for all SIMs associated to the UE while maintaining the fact that the UE only needs to monitor one paging occasion and can receive pages for all SIMs. The UE's RM state for each SIM is updated in the UE and should match that of AMF1, i.e. RM-REGISTERED for SIM1 and RM-INACTIVE for SIM2.

Indirect registration can also be performed after the UE registers each SIM in each PLMN, whether the PLMNs are the same or different. In other words, a multi-SIM UE first registers SIM1 in PLMN1, then registers SIM2 in PLMN2, and finally performs indirect registration. Note that the order of registration in PLMN1 and PLMN2 does not matter. After the SIMs are registered in their respective PLMNs, the UE can then decide to operate primarily on one of the SIMs, for example the primary SIM (e.g. SIM1) configured by the user. In this case, the UE can perform indirect registration from PLMN1 to PLMN2 via the user plane of PLMN1 for SIM2.

Figure 39 shows the procedure for a multi-SIM UE to perform indirect registration of an inactive SIM over the user plane of an active SIM. Before performing the indirect registration procedure, the UE had registered with the corresponding PLMNs individually, e.g., SIM1 in PLMN1 and SIM2 in PLMN2. The UE then performs the indirect registration procedure for SIM2 using the PDU session created for SIM1 on PLMN1. The user of the UE may have triggered this procedure by configuring the UE so that SIM1 is the preferred SIM or the user remains connected to PLMN1 for a period of time to complete an important activity and at the same time also be able to receive mobile terminated services such as paging requests for SIM2.

Step S3902: The UE registers separately with PLMN1 and PLMN2 for each SIM. As part of the multi-SIM operation, the UE monitors paging messages and periodically switches communication between the two PLMNs to ensure that the registration state of each SIM remains RM-REGISTERED.
Step S3904: The UE establishes a PDU session on PLMN1 for SIM1 to establish a data connection. One or more PDU sessions may be created. One of the PDU sessions may be established for important activities such as a voice call made by the user of the UE or an important download that the user does not want to be interrupted. Another PDU session may be associated with a general connection to the Internet that is established after the UE is registered in the PLMN. Apart from this, the UE has also established a PDU session for SIM2 on PLMN2.
Step S3906: If the SIM1 activity from step S3904 was important to the user of the UE, the user may configure via the GUI that SIM1's service is not interrupted. This configuration causes the UE to disable switching communications between the two PLMNs and remain connected to PLMN1, possibly for a configured period of time, configured location, etc. Alternatively, the user of the UE may have configured SIM1 to be the primary SIM and SIM2 to be the secondary SIM. As a result, the UE makes a decision that the user would prefer to remain connected to PLMN1.
Step S3908: As a result of the decision made in step S3906, the UE sends an indirect registration request to the N3IWF of PLMN2 via the user plane of PLMN1. The UE utilizes the address of the N3IWF2 provisioned to the UE in the PDU session created in step S3904 and the access and mobility policy delivered to the UE by the PCF from PLMN2 to send the indirect registration. The registration message may include the following information in the request: multi-SIM indicator, indirect registration indicator, SIM2 identifier, optional time period, location information, whether PLMN2 should buffer the UE's downlink data, that the UE is reachable via the user plane of PLMN1, etc. The UE may obtain its public IP address through an external mechanism (e.g., STUN protocol) and provide the address in the indirect registration message to the N3IWF2. If the UE has been assigned a unique IPv6 address or prefix, the UE can provide the address or prefix to the N3IWF2 in an indirect registration message. Alternatively, the UE can establish a secure tunnel to the N3IWF2 to enable the proposed functionality. The UE can also indicate a PDU Session ID to associate future paging requests provided by PLMN2 in a NAS notification sent to the UE via the user plane of PLMN1. The PDU Session ID can be a PDU session previously established by the UE on PLMN2.
Step S3910: AMF2 processes the registration request received from the UE through the N3IWF of PLMN2. The presence of the multi-SIM indicator informs the AMF that the UE is a multi-SIM device and indicates that the indirect registration request can reach the UE via the user plane of the PLMN from which this request originates. If a time period was provided to indicate the time the UE will remain connected to PLMN1, the AMF may reset or pause the registration timer associated with SIM2 and activate a new pause timer based on the value provided by the UE. AMF2 returns an accept response to the indirect registration that may include the status of the request, the time value for which the AMF suspends the registration of the UE, a PDU session ID that PLMN2 associates with future paging requests that will be forwarded to the UE if not provided by the UE, etc.

The procedure shown in Figure 39 allows PLMN2 to forward paging requests to the UE via the user plane of PLMN1. The UE is assumed to maintain the PDU session established on PLMN1 so that it can receive NAS notifications that may be received from PLMN2. Before releasing the PDU session on PLMN1, the UE may need to inform PLMN2 that it is no longer reachable via the user plane of PLMN1. If a secure tunnel has been created, the UE can receive paging requests as long as the secure tunnel is active.

(indirect attachment)
An alternative to partial attach in LTE is the indirect attach enhancement, as shown in Figure 25. Indirect attach can be considered as an initial attach procedure, but with added functionality to support multi-SIM operation, instead of directly in the home PLMN, it can be performed indirectly from another PLMN. In this case, an indirect attach procedure is performed through PLMN1 to SIM2. As a result, context information regarding the registration of SIM2 is established in the MME of PLMN2, and default bearers can also be created in the SGW and PGW of PLMN2. As in the case of partial attach, indirect attach can be incorporated as a general attach procedure performed in step S2502 of Figure 25, which allows paging request forwarding. Indirect attach also allocates an MME to serve the UE.

Step S2502: The UE performs an attach procedure of SIM1 to PLMN1, which is the active PLMN. This step may be performed initially when only SIM1 is installed in the UE. If two or more SIMs are installed in the UE at the same time, a combined attach procedure may be performed to register multiple SIMs together in one attach request. This combined attach request may include a multi-SIM indicator, an indirect attach indicator, appropriate SIM identifiers (e.g., IMSI, GUTI, etc.) for each SIM, and an identification of PLMN2 when the UE registers to PLMN1 for SIM1. In this case, the indirect attach is integrated as part of the attach procedure from TS 23.401 and may be referred to as MUSIM attach, which will be described later. The multi-SIM indicator may be coded as an option in the preferred network behavior parameter or may be a standalone indicator, and the indirect attach indicator may be carried in the attach type parameter. The message may further indicate which SIM is the primary SIM and which is the secondary SIM and should be used to register in the inactive PLMN. The procedure skips to step S2506 of the MUSIM Attach Request, and the requests may be performed simultaneously or sequentially, for example, registration of SIM1 followed by registration of SIM2.
Step S2504: After some time, an indirect attach procedure is initiated. For example, this can be done when SIM2 is added to the UE by inserting a physical SIM, through eSIM configuration, based on a request from an application on the UE through a GUI, or immediately after completion of the attach procedure by PLMN1. SIM2 is considered as a secondary SIM and associated with PLMN2, which is considered an inactive PLMN. The UE then performs an indirect attach request to PLMN2 through PLMN1. This request can include a multi-SIM indicator, appropriate SIM identifiers (e.g., IMSI, GUTI, etc.) for each SIM, and other PLMN identification information. The multi-SIM indicator may be coded as an option of the preferred network behavior parameter or may be a standalone indicator. The multi-SIM indicator can be used by the network entity to check and select an appropriate network entity that supports multi-SIM operation during the attach procedure and to enable paging request forwarding.
Step S2506: In response to the indirect attach request or the indirect attach indication, the MME of PLMN1 selects an appropriate MME to process the indirect attach request for the respective SIM. The identifier provided to SIM2 may include an MCC and an MNC, or may be resolved to an MCC and an MNC that are used to determine the MME to be contacted. The MME of PLMN1 may be provisioned with contact information of other MMEs of different PLMNs due to the core network configuration, roaming agreements, or other mechanisms supporting multi-SIM operation, so that the MME of PLMN1 can forward the indirect attach request to the corresponding MME.
Step S2508: MME1 sends an indirect attach request to the selected MME. The request may include an indirect attach indicator, a multi-SIM indicator, a SIM2 identifier, and other information required for the connection request. In addition, the MME1 ID and UE ID associated with SIM1 may be provided to inform the MME of PLMN2 that SIM1 has been authenticated with PLMN1. MME1 may further provide context information of the MME of PLMN1 for PLMN2 to forward a paging request for SIM2 or to receive a paging request for SIM1 from PLMN1. This MME in PLMN1 may be configured to support paging request forwarding and may be capable of forwarding the paging request from PLMN2 to an appropriate network entity (e.g., the MME to which the UE is attached in case of UE mobility) so that the UE receives the page. The MME may also forward paging requests for SIM1 from PLMN1 to PLMN2 during the time the UE is attached to PLMN2.
Step S2510: The indirect attach request is processed as outlined in steps 3 to 17 of the E-UTRAN 3202 attach procedure of TS 23.401. Note that the NAS message response sent in step S2006 is re-routed to the MME of PLMN1 instead of going to a RAN node of PLMN2. The indirect attach accept response received from this procedure includes the result status of the procedure. The response may include an indication that authentication of SIM2 was successful, a temporary identifier assigned for SIM2 by MME2 2502, an indication that the UE's EMM state for SIM2 has changed from EMM-DEREGISTERED to EMM-INACTIVE, an acknowledgement of support for receiving paging requests forwarded by PLMN1 for SIM1, contact information of the MME for receiving paging requests from PLMN1, and a registration timer for SIM2. If the indirect attach was not accepted, the response may include further information detailing why the attach was not accepted.
Step S2512: The MME of PLMN1 returns an indirect attach accept message to the UE, which may be a modified attach accept message providing additional information regarding the status of the indirect attach procedure. If the attach procedure was performed for multiple SIMs, there may be a separate registration status for each SIM. The response message may include information returned from the MME of PLMN2, such as a temporary identifier and an indication of successful authentication of SIM2. The temporary identifier assigned to SIM2 is used to identify future paging requests for SIM2 that are forwarded to PLMN1. In addition, the MME of PLMN1 may assign a separate temporary identifier for SIM2 that may be used to page the UE, instead of using the temporary identifier assigned by PLMN2. The assignment of this temporary identifier may be such that the associated paging occasion overlaps with the paging occasion associated with SIM1. As a result, the UE only needs to monitor one paging occasion to receive pages for both SIM1 and SIM2. The MME may alternatively assign the same temporary identifier to all SIMs associated with the UE while maintaining the fact that the UE only needs to monitor one paging occasion and is able to receive pages for all SIMs. The UE's EMM state for each SIM is updated. In this scenario, the EMM state for SIM1 is EMM-REGISTERED and for SIM2 is EMM-INACTIVE. Similarly, the EMM state in the MME of PLMN1 is EMM-REGISTERED for SIM1 and EMM-INACTIVE for SIM2. Finally, the EMM state in the MME of PLMN2 is EMM-INACTIVE for SIM2. Figure 25 also includes SGW2 2504 and PGW2 2506.

Similar to the indirect registration performed over the user plane in 5G as shown in FIG. 39, the indirect attach request may also be sent over the user plane in LTE. The procedure would be performed in a similar manner, but the messages and entities involved are LTE messages and entities. For example, the indirect registration message would be replaced with an indirect attach message, and the message would pass through the LTE RAN, SGW/PGW, ePDG, and MME. The LTE RAN and SGW/PGW are associated with PLMN1, while the ePDG and MME are associated with PLMN2. The policy may come from the Access Network Discovery Selection Function (ANDSF) policy of PLMN2.

(MUSIM registration/attachment)
Another enhancement of both 5G and LTE systems to support multiple SIMs is through the introduction of the MUSIM registration or attach procedure, which allows the UE to register multiple SIMs in the same registration or attach request. This MUSIM registration or attach procedure can support registration of SIMs to the same or different PLMNs, depending on which operator issued the SIM. For SIMs acquired from the same operator, the SIMs may be registered in the same PLMN, and within the PLMN, individual UE contexts are created, one for each SIM. In addition, the UE contexts can be linked together to provide optimization when forwarding paging requests. For SIMs acquired from different operators, the UE can register the SIMs associated with the active PLMN and then request the network to register SIMs from other operators with their associated PLMNs. When registering SIMs in different PLMNs, the core network can use either the partial or indirect registration/attach procedures described above. Figure 26 illustrates an example MUSIM attach procedure in more detail. Note that although the figure uses terminology associated with LTE, the procedure may also be applied to 5G systems.

Step S2602: Two SIMs are installed in a MUSIM-enabled UE: SIM1 is the primary SIM and is associated with PLMN1, and SIM2 is the secondary SIM and is associated with PLMN2. Note that although the figure shows only two SIMs, it is understood that more than two SIMs may be installed in the UE and the procedure remains the same except that the attach procedure is extended for each installed SIM.
Step S2604: The UE executes a MUSIM attach request, which results in each installed SIM being registered with the associated PLMN. The request may include the following, i.e., a multi-SIM indicator and an identifier for each SIM, in addition to other data required for the attach procedure. In addition, either a partial or indirect attach indication may be provided to inform the MME of PLMN1 how to register the SIMs associated with different PLMNs. This indication may be provided per SIM or collectively for all SIMs. If the attach procedure from TS 23.401 is enhanced to integrate the MUSIM functionality proposed here, the multi-SIM indicator may be coded as an option in the preferred network behavior parameter or may be a standalone indicator, and the partial/indirect attach indicator may be carried in the attach type parameter. The message may further indicate which SIM is the primary SIM and which is the secondary SIM and should be used to register with the inactive PLMN.
Step S2606: The MME of PLMN1 performs an attach procedure for the primary SIM. The UE is authenticated and authorized, and a registration context is created on MME1 for SIM1. This procedure may also create a default bearer for the UE in the SGW and PGW of PLMN1. Since SIM1 is the primary SIM, if the attach is successful, the EMM state of SIM1 in the MME is set to EMM-REGISTERED.
Step S2608: The MME of PLMN1 may also register other SIMs belonging to the same operator as SIM1. If SIM2 belongs to the same operator as SIM1, an attach procedure is performed for SIM2 and a registration context for SIM2 is created in the MME separate from the registration context for SIM1. However, the UE contexts may be linked together to provide optimization when forwarding paging requests. If the attach is successful, the EMM state of SIM2 becomes EMM-INACTIVE since it is not the primary SIM of the UE. This step may be repeated for multiple SIMs belonging to the same PLMN as SIM1. In this particular case, SIM2 belongs to another PLMN, so step S2608 is skipped.
Step S2610: The MME of PLMN1 performs either partial or indirect attach for SIM2 with PLMN2. The UE may have provided an indication of which attach request to perform in step S2604, or the MME may have been configured on which attach procedure to perform, or the core network may have a system policy indicating which attach procedure to perform. The MME of PLMN1 now sets the EMM state of each SIM to EMM-INACTIVE. The EMM state of each SIM of each PLMN is also set to EMM-INACTIVE. The information exchanged between PLMN1 and PLMN2 is the same as that specified previously, and may be in a NAS container encrypted for certain information to protect the privacy of the UE.
Step S2612: The MME of PLMN1 aggregates all the attach acceptance results of each SIM and returns them to the UE. Instead of using the temporary identifiers assigned by other PLMNs, the MME of PLMN1 can assign a separate temporary identifier for each SIM that can be used to page the UE. The assignment of these temporary identifiers can be such that the associated paging occasions overlap or are close to the paging occasions associated with the primary SIM. As a result, the UE only needs to monitor paging occasions that are close to each other in order to be able to receive the pages of all SIMs. The MME can alternatively assign the same temporary identifier to all SIMs associated with the UE, so that the UE only needs to monitor one paging occasion but can receive the pages of all SIMs. Upon receiving the attach acceptance, the UE sets the appropriate EMM state for each SIM. In this particular case, the EMM state in the UE for SIM1 is EMM-REGISTERED and for SIM2 it is EMM-INACTIVE.

5G Registration States for Multi-SIM Operation
To support multi-SIM operation in 5GS, a new Registration Management (RM) state is proposed. The new state called RM-INACTIVE refers to the RM state of a UE with an inactive PLMN. Furthermore, the state represents the fact that the PLMN has authenticated the SIM for use in the core network. Any existing UE context and PDU sessions in the core network associated with the SIM/UE are maintained as if the UE was in RM-REGISTERED, CM-IDLE, and RRC_IDLE or RRC_INACTIVE states. Therefore, when the UE is in RM-INACTIVE state, it also needs to be in CM-IDLE and RRC_IDLE or RRC_INACTIVE states.

RM-INACTIVE state means the following (see SIM and PLMN in Figure 9):
- The UE is registered with PLMN2 for SIM2 and is able to receive services from PLMN2 (e.g. voice or IMS calls, SMS messages, etc.).
- The UE is in CM-IDLE state and has no NAS signalling with the core network of PLMN2.
- The UE is not attached to any RAN node in PLMN2 and therefore is not monitoring paging occasions from PLMN2 for SIM2.
- The UE can receive a paging request for SIM2 when it is forwarded by PLMN2 to PLMN1.
The AMF (or UDM) in PLMN2 can page the UE by forwarding a paging request for SIM2 to the AMF in PLMN1.
- AMF in PLMN2 does not know the UE's location.
A security context may be stored in the AMF in PLMN2 to protect NAS messages between the UE and PLMN2.

Figure 14 shows the RM management states updated to include the RM-INACTIVE state. The UE can transition to the RM-INACTIVE state from the indicated RM states by performing the procedures listed.
From RM-DEREGISTERED state to RM-INACTIVE state:
o Executing a partial registration procedure o Executing an indirect registration procedure From RM-REGISTERED state to RM-INACTIVE state:
o Executing SIM switching (e.g. periodic registration update) procedures

The UE can transition from the RM-INACTIVE state as follows:
RM-INACTIVE to RM-REGISTERED state: o Performing a registration procedure o Performing a SIM switching (e.g. periodic registration update) procedure RM-INACTIVE to RM-DEREGISTERED state: o Performing a deregistration procedure (initiated by either the UE or the network)
- The core network may initiate a de-registration procedure if the UE does not perform a periodic registration update in a timely manner when in RM-INACTIVE state (e.g. the registration timer (in multi-SIM policy) expires before the UE performs the periodic registration update procedure).
If the registration update request fails

When the UE performs the SIM switching procedure and the switching is accepted by the core network, the UE's RM state transitions from RM-REGISTERED to RM-INACTIVE. However, if the switching is rejected, the UE's RM state transitions to RM-DEREGISTERED.

In the above discussion, it has been proposed to update the RM state model to include a new state RM-INACTIVE. However, introducing a new state into the state model can lead to complications in the UE implementation. As a result, the new RM-INACTIVE state may be considered as a sub-state of the RM-REGISTERED state or as a mode of operation within the RM-REGISTERED state, since both the RM-INACTIVE and RM-REGISTERED states presume that the UE is registered in the core network and can receive services from the core network. Furthermore, many of the characteristics of the RM-INACTIVE state are similar to those of the RM-REGISTERED state. However, one main difference is that the UE is not actively monitoring for paging opportunities from inactive PLMNs, and therefore paging request forwarding is required. RM-INACTIVE may be referred to as a "registered inactive" substate or mode of operation of the RM-REGISTERED state. Thus, this "registered inactive" substate or mode may replace the RM-INACTIVE state referenced in FIG. 14 and elsewhere in this disclosure.

LTE Mobility Management States for Multi-SIM Operation
Similarly, Enhanced Mobility Management (EMM) states in LTE provide similar functionality to that of the 5GS registration management states. To support UEs to register secondary SIMs with their corresponding PLMNs, a new EMM state is proposed to inform all entities of the status of their secondary SIMs' registration. The new state, EMM-INACTIVE, captures the fact that a secondary SIM is registered with a PLMN, but the UE is not actively communicating with that PLMN. Active communication refers to the fact that the UE is in EMM-REGISTERED state and can be in either ECM-IDLE or ECM-CONNECTED state. In other words, the UE can receive NAS notifications or be paged from the core network. Even when not actively communicating with the PLMN, a UE context can be stored in the PLMN for the UE to receive, for example, phone messages or short messages.

The EMM-INACTIVE state means the following (see SIM and PLMN in Figure 25):
- The UE is registered with PLMN2 for SIM2 and is able to receive services from PLMN2 (e.g. voice or IMS calls, SMS messages, etc.).
- The UE is in ECM-IDLE state and has no NAS signalling with the core network of PLMN2.
- The UE is not attached to any RAN nodes in PLMN2 and therefore is not actively monitoring paging requests from RAN nodes in PLMN2 to SIM2.
- The UE can receive a paging request for SIM2 when it is forwarded by PLMN2 to PLMN1.
- The MME (or HSS) in PLMN2 can page the UE by forwarding the paging request for SIM2 to the MME in PLMN1.
- The MME in PLMN2 does not know the UE's location.
- The security context is stored in the MME of PLMN2 and is used to protect messages from PLMN2 to the UE.

Figure 27 shows the EMM state model incorporating a new state EMM-INACTIVE state. This state transition model is implemented in both the UE and the MME. The UE can transition from the indicated EMM states to the EMM-INACTIVE state by performing the listed procedures.
From EMM-DEREGISTERED state to EMM-INACTIVE state:
o Performing a partial attach procedure o Performing an indirect attach procedure From EMM-REGISTERED state to EMM-INACTIVE state:
o Performing a SIM switching (e.g. registration update request) procedure

The UE can transition from EMM-INACTIVE state as follows:
EMM-INACTIVE state to EMM-REGISTERED state:
o Performing an Attach procedure o Performing a SIM Switching (e.g. Registration Update Request) procedure From EMM-INACTIVE state to EMM-DEREGISTERED state:
o Execution of detach procedure (either UE or network initiated)
If the UE does not update the attach timer periodically while in EMM-INACTIVE state, the core network may initiate a detach procedure.
If the registration update request fails

When the UE performs the SIM switching procedure and the switching is accepted by the core network, the UE's EMM state transitions from EMM-REGISTERED to EMM-INACTIVE. However, if the switching is rejected, the UE's EMM state transitions to EMM-DEREGISTERED.

In the above description, it has been proposed to update the EMM state model to include a new state, EMM-INACTIVE. In theory, the proposed new state provides a clear delineation of the functionality from the existing states and provides new functionality introduced by supporting multiple SIM UEs. However, in practice, the new state may not be feasible given the existing deployment. To that end, the new EMM-INACTIVE state may be considered as a sub-state of the EMM-REGISTERED state or as a mode of operation within the EMM-REGISTERED state, since both states presume that the UE is registered in the core network and can receive services from the core network. Furthermore, many of the characteristics of EMM-INACTIVE are similar to those of the EMM-REGISTERED state. However, one main difference is that the UE is not actively monitoring paging requests on the inactive PLMN, and therefore paging request forwarding is required. Referring back to the example of FIG. 25, the UE is in EMM-REGISTERED state with PLMN2 (for SIM2) but is operating in an "inactive registration" sub-state or mode that requires PLMN2 to forward any paging requests to the UE through PLMN1. Thus, EMM-INACTIVE can be considered an "inactive registration" sub-state or mode of the EMM-REGISTERED state. This "inactive registration" sub-state or mode can therefore replace the EMM-INACTIVE state referenced in FIG. 27 and elsewhere in this disclosure.

The EMM states of each SIM of a UE may be combined in the UE to provide optimized operation that reduces power consumption for multi-SIM operation. For example, instead of performing PLMN and cell selection for each SIM, a multi-SIM UE may minimize power consumption by only performing PLMN and cell selection for the active SIM or target PLMN when attempting to connect to that PLMN after a SIM switching procedure. Similarly, certain timers such as DRX timers and other NAS timers may not need to be maintained for inactive SIMs. Table 3 shows an example of a two SIM UE, where optimizations may be realized based on the EMM states of each SIM. Note that while the table shows the case of two SIMs, it can be easily extended to support more than two SIMs. Some of the state combinations are temporary, such as EMM-INACTIVE states for both SIMs, which may occur temporarily during a SIM switching procedure.

Multi-SIM Paging Operation
After the UE has registered and linked the registration status of SIM1 and SIM2 to the corresponding PLMNs, a paging request associated with either SIM is sent to the UE on the active PLMN. Within each PLMN, the registration status of each SIM may be stored and linked together to inform the PLMN that the SIMs belong to the same UE. Figure 15 shows an example of a page originating in PLMN2, an inactive PLMN, and received by the UE through PLMN1, an active PLMN. Within PLMN1, the registration status of SIM1 is RM-REGISTERED and the registration status of SIM2 is RM-INACTIVE (or an "inactive registration" sub-state or mode of RM-REGISTERED). In addition, PLMN1 may maintain a temporary identifier mapping between the SIMs so that paging requests can be forwarded from PLMN2 to the UE.

Step S1502: The UE is performing either partial registration or indirect registration of SIM2 with PLMN2 to have the page of SIM2 transferred to PLMN1 when the UE's RM state with PLMN2 is RM-INACTIVE. The UE is in RM-REGISTERED and CM-IDLE with PLMN1. The UE can provide multi-SIM support information to each PLMN of the SIMs to configure the PLMN of the user's preferences for multi-SIM operation. The multi-SIM support information is described in more detail below.
Step S1504: The UE monitors paging occasions associated with SIM1 or SIM2, e.g., whether the UE has been provided with a temporary identifier for SIM1 and another temporary identifier for SIM2 from the AMF of PLMN1. Note that the AMF may have assigned temporary identifiers such that the paging occasions calculated from each identifier overlap at the same time, which minimizes the time that the UE needs to monitor paging occasions. As a result, the UE only needs to monitor one paging occasion that applies to both SIMs. If there are three or more SIMs, the AMF may have assigned temporary identifiers such that the paging occasions do not collide with each other and may be close to each other. In these cases, the UE may have to monitor multiple paging occasions, but can still receive pages for all SIMs without paging collisions. Alternatively, the AMF may assign the same temporary identifier to all SIMs associated with the UE, so that the UE only needs to monitor one paging occasion.
Step S1506: If SIM2 is registered in partial registration, a paging request is originated in PLMN2 to SIM2 of UDM2, for example from a voice or IMS call associated with SIM2. UDM2 sends a paging request to the UE through AMF1 in step S1506, identifying that the page is associated with a temporary identifier assigned to SIM2 from PLMN2. The temporary identifier was provided to the UE at the end of the partial registration procedure. In addition, service prioritization information may be included in the paging request to inform the UE what the page is for and to help the UE decide whether to switch to PLMN2. The service prioritization information may include a service type and additional information identifying the source of the data for which the UE is paging. The service type may be a voice call, an SMS message, other data such as from an application, control plane signaling, emergency message, emergency callback, mobile terminated exception data, etc. The additional information may be the phone number of the caller or the SMS message, the PDU session ID, the slice instance ID, or the application ID associated with the data. Alternatively, the additional information may be a prioritization level configured by the user of the multi-SIM UE. The paging request may be encapsulated in an encrypted NAS container such that only the UE can decode it and may contain the contents of the NAS notification generated by PLMN2 to SIM2. The temporary identifier and possibly the service type of the service prioritization information may be unencrypted to allow PLMN1 to identify the UE to which to forward the NAS container and provide the UE with some indication of what the page is for. The contents of the NAS container of the paging request may also include an SMS message that may be sent to the UE without having the UE connect to PLMN2 to retrieve the message. If the multi-SIM support information has been provided to PLMN2, PLMN2 may decide whether to page the UE. For example, if the service prioritization information associated with the page is not configured as important to the user as reflected in the multi-SIM support information, PLMN2 does not send the paging message shown in step S1506. In some cases, PLMN2 may be configured to forward a paging request message that includes only the UE identifier and the service prioritization information. One example is for the user to configure that all paging messages should be filtered by the active PLMN, and therefore all inactive PLMNs should forward paging requests with only the information required by the active PLMN to filter the paging request.
Step S1508: Alternatively, if SIM2 is registered in indirect registration, AMF2 can receive the downlink data notification of SIM2 and forward the page to AMF1. The page can include a temporary identifier associated with SIM2 from PLMN2, as well as a service type of service prioritization information that can inform the UE what the page is for and can be used by the UE to decide whether to switch to PLMN2. The temporary identifier was provided to the UE at the end of the indirect registration procedure. As in step S1506, the paging request can include an encrypted NAS container that also accompanies the service prioritization information and the SMS message. As in step S1506, PLMN2 can use the multi-SIM support information to decide whether to forward the paging message to PLMN1 and what information to include in the forwarded paging message.
Step S1510: AMF1 processes the paging request from either step S1506 or step S1508 and generates a NAS notification to the UE. The NAS notification may include the temporary identifier of SIM2 and any service prioritization information provided. The notification may include the encrypted NAS container received from step S1506 or S1508, so that only the UE can decrypt the container and the SMS message, if provided. If the UE is in CM-IDLE state, AMF1 generates a paging request message to page the UE.
Step S1512: AMF1 sends a page with the temporary identifier associated with SIM2 to the UE via RAN1. In other words, as an example, the UE identity of the PagingRecord information element of the paging message is set to the temporary identifier associated with SIM2 from PLMN2. The temporary identifier used may be any of the identifiers specified in step S1504. In addition, the PagingRecord information element may be enhanced to provide the service prioritization information sent by AMF2 in step S1506 or S1508. The service prioritization information may include the service type (e.g., voice or IMS call, SMS message, other data for PDU session, control plane signaling, emergency message, emergency callback, mobile terminated exception data, etc.) and other information such as PDU session ID or slice instance ID, further informing the UE what the page is for. If the UE is in CM-CONNECTED state, AMF1 sends the NAS notification from step S1510 to the UE instead of a paging message. The NAS notification contains the same information as that of the paging message used to generate the paging message when the UE is in CM-IDLE. Note that AMF1 notifies the RAN node to page the UE on the paging occasion associated with SIM1, but includes the paging information associated with SIM2 received from PLMN2. If AMF1 assigned a separate temporary identifier for SIM2, AMF1 can notify the RAN node to page the UE using the temporary identifier assigned to AMF1 for SIM2, and the PagingRecord information element contains the temporary identifier assigned to AMF1 for SIM2. If the AMF1 has assigned the same temporary identifier to all SIMs of the UE, this temporary identifier is used to page the UE.
Step S1514: The UE reads the paging message and determines that the page is for SIM2 based on the temporary identifier of the UE identity information element of the paging message. The UE identity information element may include the temporary identifier assigned by PLMN2 to SIM2 or one of the temporary identifiers assigned to AMF1. If the temporary identifier is shared among all SIMs, the UE may need to perform a service request procedure to find the SIM to which the page applies. The paging message may also include an indicator that notifies the UE to perform a service request procedure to retrieve more information of what to do next. If the indicator is not present, the UE may be configured to automatically perform the service request when it determines that the page is for the UE. If the UE was in CM-CONNECTED, the NAS notification is processed and the UE makes the decision of what to do next by evaluating the service prioritization information. The UE may also process the SMS message if provided in the NAS container and present the message to the user. Therefore, the UE does not need to connect to PLMN2 to retrieve the SMS message.
Step S1516: If the UE is in CM-IDLE, the UE establishes an RRC connection with RAN1 for SIM1. The UE then performs a service request procedure with the core network to establish a NAS connection. The service request response provides the UE with more information on what to do next and may include the temporary identifier of SIM2 from PLMN2 and service prioritization information. Upon evaluating the service prioritization information, the UE may decide to perform a SIM switching procedure to complete the processing of the page and receive data associated with the page from PLMN2. If the SMS message was provided in a NAS container, the UE may present the message to the user and does not need to connect to PLMN2 to retrieve the SMS message.

Figure 15 shows the case where a UE has an active registration with PLMN1, an inactive registration with PLMN2, and may receive a paging request for SIM2 forwarded from PLMN2. Conversely, a UE may be actively registered in PLMN2 and inactively registered in PLMN1, and may receive a paging request forwarded from PLMN1. The requirement for a UE to forward a paging request from an inactive PLMN where the UE has an inactive registration is that the UE performs either partial or indirect registration with the inactive PLMN.

The service prioritization information may encompass a service type associated with a service that the core network provides to the UE for receiving downlink data, such as voice or IMS calls, SMS messages, other data (e.g., mobile terminated data such as Internet data), control plane signaling, emergency messages, emergency callbacks, mobile terminated exception data, etc. The service type prioritization information may also be associated with a priority category that specifies the source of such a service, such as a PDU Session ID, a Slice Instance ID, an Application ID, a call or message from family, friends, or a service provider, etc. Alternatively, the additional information may be a prioritization level configured by the user of the multi-SIM UE. The resulting enumeration of the service type and the priority category combined may be presented in the PagingRecord information element of the paging message to give the UE additional information on which to make a switching decision. Alternatively, the service type may determine which paging channel is being used to page the UE. Furthermore, the service prioritization information may be retrieved by the UE in response to receiving a paging request. This service type prioritization information can be compared to the service prioritization list seen in Table 4 to help the UE decide whether to switch to a service offered by the corresponding PLMN.

The multi-SIM paging operation describes the case when the UE is in CM-IDLE with an active PLMN. However, when the UE is in CM-CONNECTED, a different mechanism is needed. In that case, the active PLMN can send a NAS notification to the UE when it is in CM-CONNECTED state to inform the UE that there is pending data for an inactive SIM. This NAS notification can provide the same information as found in the paging message from PLMN2. As a matter of fact, this NAS notification can be used as a trigger event to page the UE when it is in CM-IDLE state. In other words, whenever there is a paging request for an inactive SIM, the active PLMN can send a NAS notification to the UE in CM-CONNECTED state. When the UE is in CM-IDLE state, the NAS notification results in a page to the UE.

Multi-SIM paging operation is similar in LTE. As previously mentioned, paging request forwarding allows MUSIM UEs to receive paging requests for secondary SIMs even if the UE is not actively monitoring paging occasions associated with those secondary SIMs. This functionality is made possible by successfully executing the attach procedure described above. In the scenario shown in Figure 28, the UE is actively communicating with PLMN1 using the primary SIM and has data available on the secondary SIM on PLMN2. PLMN2 forwards the paging request for the secondary SIM to PLMN1, which informs the UE that there is data for SIM2 on PLMN2. Figure 28 shows this scenario while the UE is ECM-CONNECTED with PLMN1 on SIM1.

Step S2802: SIM1 and SIM2 are installed in the UE, SIM1 is the primary SIM, and SIM2 is the secondary SIM. The UE performs either partial or indirect attach with PLMN2 for SIM2, and paging request forwarding is enabled for SIM2. The EMM state in the UE for SIM1 is EMM-REGISTERED, and for SIM2 is EMM-INACTIVE (or "inactive registration" sub-state or mode of EMM-REGISTERED). The UE can provide multi-SIM support information to the PLMN of each of the SIMs to configure the PLMN of the user's preferences for multi-SIM operation. The multi-SIM support information is described in more detail below.
Step S2804: The UE is in ECM-CONNECTED state with respect to SIM1 and is receiving data services from PLMN1.
Step S2806: Data is available for SIM2 on PLMN2. If the UE previously performed a partial attach, the HSS of PLMN2 forwards the paging request to the MME of PLMN1 in step S2806a. If the UE previously performed an indirect attach, the MME of PLMN2 forwards the paging request to the MME of PLMN1 in step S2806b. The forwarded paging request indicates that there is data for the UE on PLMN2 and may include additional information such as a temporary identifier assigned to SIM2, an identifier such as a PDU session ID, and/or an application ID associated with the data for the page, as well as a service category indicating what the page is for. The paging request includes the contents of the NAS notification generated by PLMN2 to SIM2 and may be encapsulated in a NAS container that is encrypted so that only the UE can decrypt it. The temporary identifier and possibly the service category may be unencrypted to allow PLMN1 to identify which UE to forward the container to and provide an indication of the service category of the page. The contents of the NAS container of the paging request may also include an SMS message that may be sent to the UE without having the UE connect to PLMN2 to retrieve the message. If multi-SIM support information has been provided to PLMN2, PLMN2 may use that information to determine whether to forward the paging message to PLMN1 and what information to include in the forwarded paging message.
Step S2810: The MME of PLMN1 generates a NAS notification including the encrypted NAS container from the paging request received in step S2806.
Step S2812: The MME of PLMN1 sends a NAS notification to the UE. The NAS notification includes an encrypted NAS container sent from PLMN2 informing the UE that there is data available in SIM2. The information may include other information such as a temporary identifier of SIM2, a service category associated with the data, and a PDU session ID and/or application ID of the data. If an SMS message is provided in the NAS container, the UE can present the message to the user, and thus the UE does not need to connect to PLMN2 to retrieve the SMS message.
Step S2814: The UE checks the service category to check whether the UE should switch to PLMN2 to retrieve data. The service category may be classified as voice call, SMS message, or other data (e.g., application data), control plane signaling, emergency message, emergency callback, mobile terminated exception data, etc. The UE determines that the provided service category information requires the execution of a SIM switch request, and proceeds to send a request to the MME of PLMN1. The request may be a registration update request or an enhanced TAU request, and the UE provides a SIM switch indication to inform PLMN1 that the UE wants to suspend the registration of SIM1 (e.g., set the UE state of SIM1 to EMM-INACTIVE). If the request is granted, the MME of PLMN1 sets the EMM state of SIM1 to EMM-INACTIVE (or enables the "inactive registration" substate or mode of EMM-REGISTERED state), activates paging request forwarding for SIM1, and preserves all UE contexts managed by PLMN1, including security context and existing PDN connections. Upon receiving a registration update or TAU accept response, the UE also sets the EMM state inside the UE. Note that the SIM switching procedure can be initiated by the user through the application via GUI, API, or through the UE's policy for multi-SIM operation.
Step S2816: The MME of PLMN1 sends a paging request forwarding response to either the MME of PLMN2 or the HSS, depending on the source of the original paging request from step S2806. The response can inform the MME of PLMN2 or the HSS that the UE has decided to perform a SIM switching procedure and will connect to PLMN2 to complete the processing of the page. The MME of PLMN1 can also inform the MME of PLMN2 that it has enabled paging request forwarding for SIM1. Alternatively, the response can include an indication that the page was received but that the user is not currently interested in connecting to PLMN2 to retrieve the data of the page. This may occur if the user is on an important call and does not want to be interrupted. The user can provide this indication through a GUI on the UE.
Step S2818: The UE then performs PLMN selection, reads system information, and performs cell selection of PLMN2 to attempt to connect to PLMN2. The UE may be configured to collect cell measurement information during this process and provide it to the RAN node of PLMN2 upon successful connection.
Step S2820: If the UE successfully connects to PLMN2, the UE sends a request to update the registration state of SIM2, e.g., an attach request or a service request, providing the temporary identifier assigned to SIM2 from one of the previously executed attach procedures. In addition, the UE may include the identifier sent in step S2806 to indicate the data associated with the page from step S2806. If successful, the request transitions the UE's EMM state in MME2 to EMM-REGISTERED (or disables the "inactive registration" substate or mode of EMM-REGISTERED), allowing the UE to retrieve the data associated with the paging request sent in step S2806. Upon receiving the response, the UE also transitions its internally stored EMM state to EMM-REGISTERED (or disables the "inactive registration" substate or mode of EMM-REGISTERED). The UE may also transmit the obtained cell measurements from step S2820 to a RAN node in PLMN2. These measurements may be used to assist cell planning for the operator of PLMN2.

While Figure 28 shows a paging request forwarding sent when the UE is in ECM-CONNECTED state to SIM1 in PLMN1, Figure 29 shows the same scenario with the UE in ECM-IDLE state with PLMN1. In other words, the ECM state in both the UE and the MME in PLMN1 is ECM-IDLE. When in this state, the UE monitors for paging information on paging occasions associated with the temporary identifier assigned to the UE during the attach procedure.

Step S2902: SIM1 and SIM2 are installed in the UE, SIM1 is the primary SIM, and SIM2 is the secondary SIM. The UE performs either partial or indirect attach with PLMN2 for SIM2, and paging request forwarding is enabled for SIM2. The EMM state in the UE for SIM1 is EMM-REGISTERED, and for SIM2 is EMM-INACTIVE (or "inactive registration" sub-state or mode of EMM-REGISTERED). The UE can provide multi-SIM support information to the PLMN of each of the SIMs to configure the PLMN of the user's preferences for multi-SIM operation. The multi-SIM support information is described in more detail below.
Step S2904: Since the UE is in ECM-IDLE state, the UE is monitoring paging occasions associated with SIM1 and SIM2 to receive paging requests from both SIMs. Note that the UE may have been provided with a temporary identifier for SIM1 and another temporary identifier for SIM2 from the MME of PLMN1. Thus, the MME may have assigned temporary identifiers such that the paging occasions calculated from each identifier overlap at the same time, which helps to minimize the time that the UE needs to monitor paging requests. As a result, the UE only needs to monitor one paging occasion. In the case of more than two SIMs, the MME may have assigned temporary identifiers such that the paging occasions do not collide with each other. In these cases, the UE may have to monitor multiple paging occasions, but can still receive pages for all SIMs without encountering a paging collision. In yet another case, the MME may have assigned the same temporary identifier to all SIMs of the UE, which is used to calculate paging occasions, thus minimizing the number of paging occasions that the UE has to monitor. In this case, the UE only needs to monitor one paging occasion and can receive pages for all SIMs installed in the UE.
Step S2906: Data is available for SIM2 on PLMN2. If the UE previously performed a partial attach, the HSS of PLMN2 forwards the paging request to the MME of PLMN1 in step S2906a. If the UE previously performed an indirect attach, the MME of PLMN2 forwards the paging request to the MME of PLMN1 in step S2906b. The forwarded paging request indicates that there is data for the UE on PLMN2 and may include additional information such as a temporary identifier assigned to SIM2 by PLMN2, an identifier such as a PDU session ID, and/or an application ID associated with the data for the page, as well as a service category indicating what the page is for. The paging request includes the contents of the NAS notification generated by PLMN2 to SIM2 and may be encapsulated in a NAS container that is encrypted so that only the UE can decrypt it. The temporary identifier and service category may be unencrypted to allow PLMN1 to identify which UE to forward the container to and provide an indication of the service category of the page. The contents of the NAS container of the paging request may also include an SMS message that may be sent to the UE without having the UE connect to PLMN2 to retrieve the message. If multi-SIM support information has been provided to PLMN2, PLMN2 may use that information to determine whether to forward the paging message to PLMN1 and what information to include in the forwarded paging message.
Step S2908: The MME of PLMN1 processes the information from the paging request received in step S2906.
Step S2910: The MME of PLMN1 sends a paging message to the RAN node in step S2910a using the temporary identifier assigned to the UE for SIM2 by the MME of PLMN1. The temporary identifier used may be any of the identifiers specified in step S2904. The RAN node then pages the UE in step S2910b on the paging occasions that the UE is monitoring. Since the paging occasions for both SIM1 and SIM2 are the same, the UE receives the page even though it is for SIM2. The paging message may also include service prioritization information to inform the UE what the page is for.
Step S2912: The UE then reads the paging report and determines that the page is for SIM2 based on the presence of a temporary identifier assigned to SIM2 and the service prioritization information. If the temporary identifier is shared among all SIMs, the UE may need to perform a service request procedure to find the SIM to which the page applies. The paging message may also include an instruction to inform the UE to perform a service request procedure to retrieve more information on what to do next. If no instruction is present, the UE may be configured to automatically perform a service request when it determines that the page is for the UE.
Step S2914: The UE performs a service request procedure to retrieve more information on what to do next. When performing the SR procedure, the MME of PLMN1 can provide the UE with information from the forwarded paging request received from PLMN2. This information can include the temporary identifier associated with the page, the service category of the page, and other information received from step S2906.
Steps S2916 to S2922: The UE performs steps S2814 to S2820 in FIG. 28 to complete the processing of the page, attach to PLMN2, and receive data associated with the paging request.

An alternative to step S2910a of FIG. 29 is for the MME of PLMN1 to send a paging request to the RAN node using the temporary identifier of SIM1 instead of the temporary identifier of SIM2. In this alternative approach, the paging information includes the temporary identifier of SIM1 with an instruction to inform the UE to perform a service request to get more information on what to do next. When the UE performs the service request procedure, the MME of PLMN1 provides the information that the page was for SIM2 and any additional information such as the service category of the page. This alternative approach can be used if the MME of PLMN1 cannot provide a temporary identifier for SIM2 that aligns the paging occasions of both SIM1 and SIM2 together. This is more difficult when more than two SIMs are in use. Alternatively, the MME of PLMN1 can assign the same temporary identifier for use when paging all SIMs installed in the UE. In this case, the UE only needs to monitor one paging occasion and performs a service request procedure to find out which SIM the page is for. The MME manages this by linking together the registration state of all SIMs of the UE and assigns the same temporary identifier to use for paging the UE regardless of SIM.

The paging request forwarding response shown in step S2918 of FIG. 29 may be sent without performing a SIM switching procedure for cases where the UE does not want to respond to the page. This may occur when the user is on an important call and does not want to be interrupted. The user may provide this indication through a GUI on the UE. In these cases, the paging request forwarding response is sent after the UE performs the service request procedure in step S2914 of FIG. 29, not after step S2916. The user may provide an indication that the page has been received but that the user is not currently interested in connecting to PLMN2 to retrieve the page's data.

The paging request forwarding may also be sent on the user plane if the UE has performed indirect registration on the user plane. Figure 40 shows an example of a multi-SIM UE receiving a NAS notification from PLMN2 for SIM2 via the user plane of PLMN1. The UE has already performed indirect registration with PLMN2 for SIM2 via the user plane of PLMN1, and downlink data arrives at AMF2 for SIM2.

Step S4002: The UE performs an indirect registration of SIM2 with PLMN2 via the user plane of PLMN1. The indirect registration allows PLMN2 to forward a paging request for SIM2 to the UE via the user plane of PLMN1. The UE can provide multi-SIM support information to the PLMN of each of the SIMs to configure the PLMN of the user's preferences for multi-SIM operation. The multi-SIM support information is described in more detail below.
Step S4004: Downlink data is available for SIM2 on PLMN2 and AMF2 is notified. AMF2 may evaluate the available multi-SIM assistance information provided by the UE to determine if the downlink data meets the paging filter criteria. If the criteria are met, AMF2 generates a NAS notification to send to the UE. If not, AMF2 returns a response to the source of the downlink data notification that the UE is not interested in receiving the data at this time or that the UE is not currently available. The response may indicate that the data should be buffered. The NAS notification may include a PDU Session ID associated with the downlink data or an SMS message. Other events that may cause AMF2 to generate a NAS notification to the UE may be control plane signaling of a policy update that AMF2 wants to send to the UE. This may include reminders to perform periodic registration or TAU updates, updates to URSP rules, new timer values for the UE to use, how soon the UE needs to respond to the notification, etc.
Step S4006: AMF2 sends a NAS notification to the UE through N3IWF2 via the user plane of PLMN1 in step S4006a. Depending on the connection management state of the UE, PLMN1 can send a NAS notification to the UE as a result of receiving a NAS notification from PLMN2, or PLMN1 can page the UE if the UE is in CM_IDLE state. For PLMN1, the NAS notification from PLMN2 is the mobile terminated data of the UE. It should be noted that the NAS notification or page sent by PLMN1 in step S4006b is associated with SIM1.
Step S4008: The UE evaluates the NAS notification received from PLMN1. Note that this NAS notification contains the information sent by PLMN2 in step S4006a. The NAS notification may contain service prioritization information to help the UE identify the service type associated with the data for which the NAS notification was generated in step S4006a.
Step S4010: The UE makes a service request to receive the mobile terminated data that triggered the page. If the UE determines that the service prioritization information in the NAS notification from PLMN2 sent in step S4006a is important, the UE uses one of two mechanisms to perform the service request to PLMN2. The first mechanism is for the UE to continue to use the user plane of PLMN1 to send the service request in response to the NAS notification received from PLMN2. This mechanism can be used by the UE if it remains connected to PLMN1 and wants to receive data of SIM2 via the user plane of PLMN1. The second mechanism is for the UE to switch the connection to PLMN2 and establish a connection with PLMN2. The second mechanism may be used by a UE if it is not currently receiving services in PLMN1 and would like to retrieve the data associated with the NAS notification sent from PLMN2 and subsequently continue to receive services from PLMN2, e.g. to make a call using SIM2.

(SIM switching procedure)
If the UE receives a page or NAS notification for the SIM of the inactive PLMN and the UE decides to retrieve the data associated with the page, the UE may perform a SIM switching procedure to suspend the UE's registration state and notify the active PLMN to allow the UE to establish communication with the inactive PLMN. Upon successful execution of the SIM switching procedure, the UE's registration state for the active SIM transitions from RM-REGISTERED to RM-INACTIVE. Once in this state, the core network retains all UE context including existing PDU sessions and slice allocations to allow the UE to quickly return to the RM-REGISTERED state. At this point, the UE performs a periodic registration update for the inactive PLMN and transitions the RM state with the inactive PLMN from RM-INACTIVE to RM-REGISTERED. The UE may then retrieve the data associated with the page or NAS notification. Figure 16 illustrates a SIM switching procedure performed by a UE switching from PLMN 1 to PLMN 2 due to receipt of a paging message on SIM 2. It is noted that although the SIM switching procedure illustrated in Figure 16 uses 5G terminology, the procedure is also applicable to LTE systems.

Step S1602: The UE receives the paging message as described in FIG. 15 and determines that it is a page for SIM2 based on the UE identity field of the PagingRecord information element. If the temporary identifier is shared between the SIMs of the UE, the UE may not know which SIM the page is for. In that case, the UE collects this information in step S1604 after performing the service request procedure. In addition, the UE is informed that the page corresponds to a voice or IMS call based on the new service prioritization field of the PagingRecord information element. The UE is configured to prioritize the voice or IMS call and decides to perform a SIM switching procedure. An alternative is that the user manually initiates the SIM switching procedure via a GUI, as shown in FIG. 17. The paging message may also correspond to an SMS message or a notification of the availability of downlink data for SIM2.
Step S1604: The UE establishes both an RRC connection and a NAS connection so that it can communicate with PLMN1. The UE can perform a service request procedure to retrieve information about which SIM the page is for and possibly the service category of the page. The UE can retrieve other information from the encrypted NAS container, such as the PDU session ID, slice instance ID, and/or application ID associated with the data of the page. The NAS container can also contain the SMS message of the page. Based on this information, the UE decides to perform a SIM switching procedure. The decision can be triggered by the user through a GUI on the UE or possibly by an application or policy on the UE.
Step S1606: The UE then performs a SIM switching request procedure where the registration type is set to SIM switching or a SIM switching indicator is included in the request. The SIM switching procedure can be incorporated as a periodic registration update with a SIM switching indication. The request is to inform PLMN1 that the UE wants to suspend its registration state and connect to PLMN2 to retrieve data associated with a page or use a service provided by PLMN2.
Step S1608: AMF1 processes the request and updates the RM state of SIM1 to RM-INACTIVE. All UE contexts managed by PLMN1, including existing PDU sessions, are preserved until the UE performs a registration update and returns to RM-REGISTERED state. Paging request forwarding is activated appropriately in UDM1 912 and/or AMF1 904 depending on whether partial registration or indirect registration was previously performed.
Step S1610: AMF1 returns a registration stop message to the UE indicating that the UE's RM state for SIM1 has changed to RM-INACTIVE. Alternatively, the message may be a registration deactivation accept message. The message may include a registration timer value to indicate to the UE that the PLMN1 will maintain the RM state of SIM1 at RM-INACTIVE for a period of time.
Step S1612: The UE transitions its RM state from RM-REGISTERED to RM-INACTIVE for SIM1 and notifies it of a registration timer value if one was provided. If there is no registration timer value, the UE may use the value provided in the internal configuration in the UE policy or configured by the user in the GUI.
Step S1614: The UE performs PLMN selection, reads system information, and performs cell selection for PLMN2. The UE then performs a registration update procedure for SIM2, which may include a SIM switching indication. The RM state of SIM2 in the UE transitions from RM-INACTIVE to RM-REGISTERED upon receiving the registration accept message, and the UE can receive voice or IMS calls from PLMN2.

(Management of registration timer for inactive SIMs)
After the secondary SIM attach procedure is successfully performed, the UE may need to periodically notify the corresponding PLMN to update the registration timer in order to keep the EMM state in EMM-INACTIVE (or the "inactive registration" sub-state or mode of EMM-REGISTERED). To do this, the UE may request to update the registration timer on the secondary PLMN through the active PLMN, rather than disconnecting from the active PLMN and connecting to the secondary PLMN to perform the inactive registration timer update request. The UE may perform a single registration timer update request, which may be an enhanced TAU request that combines the registration timer updates in both the active and secondary PLMNs, as shown in Figure 30 for the two SIM case. Alternatively, the UE may request the active PLMN to forward the inactive registration timer update (IRTU) request separately to the secondary PLMN if there is activity on the active PLMN that does not require a registration timer update. It should be noted that the procedure shown in FIG. 30 is for an LTE system, and the procedure may also be applied to a 5G system.

Step S3002: The UE sends a TAU request to the MME of PLMN1 to update the registration timer maintained in PLMN1 for SIM1. The request may include a temporary identifier assigned by PLMN1 to SIM1, a multi-SIM indicator, a temporary identifier assigned by PLMN2 to SIM2, and other parameters of the TAU request. This indicates to the MME of PLMN1 not only to update the registration timer for SIM1 in PLMN1, but also to forward an IRTU request to PLMN2 for SIM2. It is noted that the multi-SIM indicator may be integrated into existing parameters such as preferred network behavior, as described above.
Step S3004: The MME of PLMN1 may perform a TAU request for SIM1 and assign a new temporary identifier to the UE of SIM1. HSS1 3002 may also be included in this step.
Step S3006: Further, the MME of PLMN1 sends an IRTU request to the MME of PLMN2 to update the registration timer of SIM2. The IRTU request may include the multi-SIM indicator and the temporary identifier assigned to SIM2 by PLMN2. It is also noted that the MME of PLMN1 can provide the location information of the last visited TAI parameter to convey the UE's location, so that PLMN2 can track the UE. Note that the IRTU request may be realized as a TAU request or a standalone request.
Step S3008: The MME of PLMN2 performs an IRTU request for SIM2 and updates the UE context for SIM2 with the information provided in step S3006.
Step S3010: An IRTU acceptance response with the status of the request is returned to the MME of PLMN1 and a new temporary identifier such as GUTI may be assigned to the UE for SIM2. Other location-dependent information such as new timer values and updated TAI lists may also be provided. In 5GS, new UE policies may be provided in the response to the UE. PLMN2 may also provide an indication that the registration status of SIM2 is no longer valid and that the UE may need to re-register with PLMN2. This information may be provided in an encrypted NAS container so that only the UE can decrypt it.
Step S3012: The MME of PLMN1 aggregates the TAU accept message with the IRTU accept message and returns it to the UE. The response may include an encrypted NAS container with the information returned from PLMN2.
Step S3014: If a new temporary identifier is assigned to either SIM1 or SIM2, the UE returns a TAU with an IRTU complete message to the MME in PLMN1.
Step S3016: If a new temporary identifier is assigned to SIM2, the MME of PLMN1 forwards the IRTU complete message received from the UE to the MME of PLMN2.

Providing Cell Measurements Obtained from SIM Switching Procedures
There may be cases where the UE attempts to perform a SIM switching procedure in an inactive PLMN and the UE is unable to establish a connection with the cell of the inactive PLMN. The cell of the inactive PLMN may be overloaded or the UE may be in an area with a coverage hole of the inactive PLMN. In these cases, the UE may proactively provide measurements found in the Minimization of Drive Test (MDT) report to the inactive PLMN through the active PLMN that may be used to improve cellular coverage. The measurements may be further transmitted to the NWDAF of the inactive PLMN for use in analysis. Figure 31 shows the case where the SIM switching procedure to connect to PLMN2 fails and the UE reconnects to PLMN1 and provides cell measurements and cause codes that are forwarded to PLMN2. The forwarding of the cell measurements and cause codes may signal that the UE is unable to further process the page.

Step S3102: After receiving the page or NAS notification, the UE performs a SIM switching procedure to disconnect from PLMN1 and attempts to connect to PLMN2. The UE may be configured to collect cell measurements while performing cell selection to attempt to connect to PLMN2. These measurements may then be stored and provided to PLMN2 at some point in the future to help characterize the signal strength of various cells belonging to PLMN2.
Step S3104: The UE attempts to connect to a cell belonging to PLMN2, but the connection fails, perhaps because the cell is overloaded, has a relatively low signal power that makes it difficult to maintain a connection, or there may even be no nearby cells that provide coverage to the UE. At the same time, the UE collects cell measurements during this process, and the UE may be provided with a cause code from the RAN2 node 906 as to why the UE failed to connect to the cell. If there is no available cell, the UE may be configured with a cause code indicating that this is the case. It is also noted that the failure may be attributable to the MME, and a corresponding cause code may be returned from the MME to the UE.
Step S3106: The UE cannot connect to the cell belonging to PLMN2, so it reconnects to the cell belonging to PLMN1.
Step S3108: The UE then sends a SIM switching request to the MME of PLMN1, providing the collected cell measurements for the cells of PLMN2. These measurements may be provided in an encrypted NAS container so that only PLMN2 can decrypt them. An indication may be provided to inform the MME of PLMN1 that there is data to be transferred to the MME of PLMN2. A cause code may also be provided as the reason why the UE was unable to connect to the cell belonging to PLMN2. This cause code may be used to inform PLMN2 that the UE attempted to complete processing of the page request but was unable to establish a connection with the cell of PLMN2. In addition, the identifier provided by PLMN2 in step S2806 of FIG. 28 to associate with the page may be included to inform PLMN2 that the UE was unable to retrieve the data belonging to this page.
Step S3110: The MME of PLMN1 processes the SIM switching request and re-activates the UE context stored in the MME of SIM1, sets the EMM state to EMM-REGISTERED (or disables the "inactive registration" sub-state or mode of the EMM-REGISTERED state), and deactivates paging request forwarding for SIM1.
Step S3112: The MME in PLMN1 forwards the encrypted NAS container obtained from the UE to the MME in PLMN2 using the cause code and identifier received in step S2806 of Fig. 28 associated with the page. This step is conditional and is only performed if the UE previously performed an indirect attach of SIM2 in PLMN2.
Step S3114: A response is returned to the UE indicating the status of SIM switching with PLMN1 for SIM1. The response may indicate the status of transfer of cell measurements and cause codes to PLMN2.

(Interworking with Multi-SIM UE)
A multi-SIM UE may support connection to both LTE and 5GS networks. It should be appreciated that the enhancements proposed herein may be applied to interworking scenarios including UE switching between LTE and 5G and from 5G back to LTE. Figure 32 shows a non-roaming interworking architecture between 5GS and EPS, where the N26 interface connects the MME in LTE with the AMF in 5G. Also, the HSS+UDM 3204 connects with the MME and AMF via interfaces S6a and N8, respectively. These interfaces may be used to support the attach procedure as well as the paging request forwarding functionality proposed herein.

(Impact of Multi-SIM on 5G UE Policy)
Currently, the UE policies stored in the UE encompass ANDSP and URSP policies to assist the UE in making access network and user route selection decisions, respectively. The UE policies are delivered to the UE by the PCF via AMF and NAS messaging. To support multi-SIM UEs, it is proposed to introduce a new policy type in the UE policies, namely the Multi-SIM policy. This new policy defines aspects of UE operation with multi-SIM capability. An example of the proposed Multi-SIM policy is shown in Table 4.

Some of the information in the multi-SIM policy may be pre-provisioned in the UE, or determined by the UE, configured by the user via a GUI, obtained by the UE from the core network, or a combination thereof. New multi-SIM policies may be created manually by the user or dynamically by the UE for each installed SIM. A list of multi-SIM policies may then be presented in the GUI, as shown in FIG. 17.

Alternatively, the multi-SIM policy may be created by the core network after the UE successfully registers with a PLMN. The multi-SIM policy that the PCF sends to the UE may be PLMN-based. In other words, the PCF of each PLMN with which the UE communicates may send a multi-SIM policy to the UE. Then, as the UE registers with other PLMNs, the new multi-SIM policy is added to the UE's policy, and the GUI shown in FIG. 17 may summarize all PLMNs in which the UE is registered. The user may then assign a priority to each PLMN and manually configure other parameters associated with that PLMN. Receipt of the new multi-SIM policy may trigger the UE to attempt a partial or indirect registration procedure, as previously described in this disclosure.

The UE can provide the core network with the radio capabilities of the UE to help the network improve multi-SIM operation. With knowledge of the radio capabilities of the UE, the core network can adjust the paging strategy used to ensure that the UE can receive paging requests while also minimizing the use of network and paging resources. The UE can have single Rx, single Tx capability, which indicates that the UE can only receive downlink signaling for one SIM at a time and can send uplink signaling to the network for one SIM at a time. A UE with dual Rx, single Tx capability can receive downlink signaling from up to two SIMs at a time, but can only send uplink signaling for one SIM at a time. The core network can provision the UE with a multi-SIM policy based on the radio capabilities of the UE during registration. This helps ensure consistent network operation for multi-SIM UEs and can help the network manage paging resources more efficiently. For example, the network can adapt the paging occasions of a single-Rx UE by sending the UE paging area information for a particular SIM. Upon receiving the paging area information, the UE can compare the received paging area with the paging areas of another SIM to determine if a potential paging collision may exist. If a potential paging collision exists, the UE can request another paging occasion for the SIM from the core network.

Instead of the UE radio capabilities being included as part of the multi-SIM policy, it may be a separate indicator provided by the UE to the core network during registration. The presence of this indicator allows the core network to manage paging occasion allocation based on the UE's radio capabilities. For dual-Rx capable UEs, the core network may assign temporary identifiers associated with random paging occasions. For single-Rx capable UEs, the core network may use the multi-SIM support information as described below to adapt paging occasions of different SIMs to avoid paging collisions.

Within the multi-SIM policy, a service prioritization list may be configured by the user of the multi-SIM UE to indicate the priority of multi-SIM traffic, such as which is the primary SIM, which type of service is of higher priority and the network should page the UE, which type of service is of lower priority and the network should not page the UE, the time period during which the UE should prioritize traffic from a particular SIM, location information, etc. The multi-SIM assistance information utilizes the user preferences from the service prioritization list and provides additional information to assist the core network in ways to enhance or optimize network operation for the multi-SIM UE. The assistance information may inform the core network which traffic is important to the UE and therefore should page the UE, which traffic is not important to the UE and should be ignored by the network by not paging the UE, how the network can assign new temporary identifiers to avoid paging collisions and which parameters to use when assigning new parameters, how long to enable filtering of paging requests by the core network, etc.

The information presented in the service prioritization list may be used to assist the UE in making a decision on what to do upon receipt of the service type information of the paging request. The service type information may provide high-level information such as voice call, SMS message, other data, control plane signaling, emergency message, emergency callback, mobile terminated exception data, etc. The UE may check whether the service type provided in the paging request matches the service type in the service prioritization list. If there is a match, the UE may decide to perform a SIM switching procedure to retrieve the data associated with the page. However, if the service type provided in the paging request is not found in the service prioritization list, the UE may respond to the page that it is currently busy, and paging request filtering may also be enabled.

In some cases, the UE may want more granular information of what the page is for to make better decisions. For example, calls from family and close friends are of more interest to the user than calls from telemarketers or robo-callers. Hence, prioritization level information can be included in the service prioritization list to specify finer granularity of the services that the user is interested in. This information may be provided by user configuration via GUI upon initial installation of multiple SIMs in the UE. The user may group users such as family, friends, colleagues, acquaintances, contractors, etc. and assign priorities to certain groups, e.g., only family and friends. Alternatively, the groups may be organized with priority levels as numerical values such as levels 1, 2, 3, etc.

The service prioritization list may include both service type categories and service prioritization levels as shown in Table 5 to enable the UE to determine whether a page is important to the user. The service type categories may consist of voice calls, SMS messages, other data, control plane signaling, emergency signaling, emergency callback, mobile terminated exception data, etc. There may be different priorities for each service type. For example, there may be levels such as levels 1, 2, and 3 assigned to voice calls and SMS messages to specify whether the calls are from the user's family and friends, from the user's contacts, or from sources that are not the user's contacts. Similarly, there may be high and low levels assigned to other data and control plane signaling for the UE, as well as other indications to describe emergency signaling. There may be one level, as in the case of emergency callback and mobile terminated exception data. Both of these cases may refer to the cases where the core network has data that is important to the UE.

As mentioned above, the service type category and the service prioritization level may be included in the paging message received by the UE. The UE may use a user-configured service prioritization list and may use the service type category and the prioritization level to make a decision as to whether the data associated with the page is of interest to the user and to help the UE decide how to respond to the page. For example, the UE may determine that the data associated with the page is important to the user and decide to perform a SIM switching procedure. Conversely, the UE may determine that the data is not that important to the user and inform the PLMN that the UE is busy or unreachable. In other cases, the UE may present the service type and prioritization level information to the user via a GUI and let the user decide how to proceed.

Some of the service prioritization levels may not be readily available to the network prior to UE registration, such as the prioritization levels for voice calls and SMS messages. These levels of people with appropriate contacts may be provided to the network by the UE via the application server after UE registration. This may be done through an API exposed to the application server to allow the user to configure different priority levels as shown in Table 5. Alternatively, the user can dynamically provide this information in the service request procedure or via the user plane by tagging the service with the appropriate level. For example, a GUI can display to the user the priority level to associate with the phone number after a voice call. The UE can then signal the indicated priority level of the voice call to the core network via the user plane.

Once the user configures the service prioritization list, the UE can utilize the user preferences to derive multi-SIM support information for the multi-SIM policy to provide to the core network. The multi-SIM support information can provide the core network with a set of service types and priorities for filtering pages to the UE to minimize waste of network and paging resources. In addition, other information in the multi-SIM support information may be provided to request different paging opportunities for the UE to monitor between installed SIMs to better avoid paging collisions. The support information may be configured by the network policy sent to the UE and is described in more detail below.

The multi-SIM support information may be provided to the core network initially during registration or as needed whenever the UE detects a need to inform the core network of such information. For example, when a user of the UE requests to use a service of a particular SIM for a certain period of time, such as an important voice call, the UE may provide the multi-SIM support information in a service request or registration update request. The support information may then be used by the core network to filter pages of services that are not of interest to the user and page the UE only for the more important services. Similarly, after the user has ended the voice call, the UE may remove or disable the support information to allow the core network to page the UE for all services.

Figure 41 shows an example of how a multi-SIM UE provides a user configuration to the core network with preferences for how the user wants the UE to operate for multi-SIM operation. After installing multiple SIMs in the UE and powering on the UE, the GUI prompts the user to configure the preferences for the UE to follow. Once the user is finished with the configuration, the UE performs registration for each of the SIMs installed in the UE. Figure 41 shows the registration of one of the SIMs and how the user configuration is sent to the core network in the form of a multi-SIM policy.

Step S4102: A user installs multiple SIMs in the UE, and upon power-on, the UE prompts the user via a GUI to configure information for multi-SIM operation. The information provided by the user can be used to specify the user's preferences for how the UE manages multi-SIM operation on the UE. These preferences can be captured in the service prioritization list of the multi-SIM policy shown in Table 4. The UE can then add the user preferences to the multi-SIM policy and provide the policy to the CN to enable enhanced handling of multi-SIM traffic. In addition, the UE can provide information that it can access, such as SIM identifier, PLMN ID and name, UE radio capabilities, maximum number of SIMs, and PLMN list, to derive the multi-SIM policy.
Step S4104: After the user configures the service prioritization list, the UE sends a registration request to the RAN node with the multi-SIM policy shown in Table 4, including the multi-SIM indicator and multi-SIM support information incorporating the user configuration. The multi-SIM indicator and multi-SIM support information can also be included in the access stratum message so that the RAN node can read the indication and information and take them into account during AMF selection.
Step S4106: Then, the RAN node selects an AMF that supports the multi-SIM UE based on the presence of the multi-SIM indicator.
Step S4108: The RAN node forwards a registration request to the selected AMF with the multi-SIM indicator, multi-SIM support information, and the remaining information elements of the multi-SIM policy.
Step S4110: The AMF performs UE registration and authentication procedures from TS 23.502 [2]. During this process, the AMF and PCF can provide additional information to the multi-SIM policy. The AMF can provide temporary network identifier(s) and a registration timer value, and the PCF can provide whether the network supports dual RM-REGISTERED operation. Dual RM-REGISTERED support indicates that the network can link multiple SIMs from the UE together, providing optimization of multi-SIM operation. For example, the network may be able to reallocate a temporary UE identifier to change the associated paging occasion if the UE requests such a change. Support may also include forwarding paging requests from one SIM to another SIM and other multi-SIM enhanced paging occasions, as described in this disclosure.
Step S4112: The AMF returns a registration acceptance response to the UE, including the update to the multi-SIM policy made in step S4110.
Step S4114: The UE internally updates the multi-SIM configuration based on the updated multi-SIM policy received from step S4112. The UE may present the policy to the user via a GUI showing all updates to the multi-SIM policy and prompt the user to confirm the updated policy.
Step S4116: If the user is prompted and confirms the multi-SIM policy, the UE may return a registration complete message to the AMF. If the UE detects that there is a possibility of paging collision between multiple SIMs based on the paging occasions of each SIM, the UE may return an indication of the registration complete message to request the AMF to assign new temporary identifiers corresponding to different paging occasions to avoid paging collisions. The UE may provide other multi-SIM support information described below to assist the AMF in assigning new temporary identifiers.

It should be noted that the inclusion of the multi-SIM policy may be provided during any of the registration procedures, whether it be initial registration, periodic registration update, partial registration, indirect registration, etc. If the UE is not able to provide the entire multi-SIM policy to the network, components of the multi-SIM policy, such as the multi-SIM support information, may be provided separately to the core network. In addition, the multi-SIM support information may be signaled to the core network whenever the UE wishes to request special handling of multi-SIM traffic. This may include adding the multi-SIM support information to a service request or a PDU session establishment or modification procedure. The multi-SIM support information may also be provided during a SIM switching procedure to inform the core network how to filter paging requests while the UE is absent from the network.

For LTE, the multi-SIM support information may be realized as context information maintained inside both the UE and the MME. Table 6 shows an example of adding the service prioritization list and the multi-SIM support information to the UE's information store stored internally as UE context. These information may be included in the attach procedure when the UE first registers with the core network, or may be provided as needed in a service request to dynamically enable paging request filtering. Similarly, the MME may store the support information in the mobility management context of each multi-SIM UE. If necessary, some of the multi-SIM support information may also be stored in the HSS.

Multi-SIM UE Support for MNOs without Coordination
Although the solutions previously described in this disclosure address paging collisions occurring in two or more SIMs, the solutions require some coordination between the MNOs. In some deployments, the MNOs may not have any coordination with each other, e.g., there is no signaling between network functions of different MNOs, such as between AMFs or MMEs of different MNOs. For these cases, other solutions are proposed below to address the paging collision problem faced by multi-SIM UEs. However, it should be noted that some aspects of the solutions described above may be applicable in the case without MNO coordination considered below. For example, the core network solution of assigning temporary identifiers to multiple SIMs of a UE whose paging occasions are aligned still applies. This is detailed when reintroducing the multi-SIM indicator presented below. The solutions described below are also applicable in the case with MNO coordination. As an example, in the registration procedure in the case with MNO coordination, the paging criteria described below may be used. The paging criteria may be used by the core network to decide whether to page the UE after receiving a forwarded paging request. Finally, although the following solutions are described for 5GS, it is expected that they may also be applied to LTE systems with related changes in network entities, procedure names, etc.

Even in the absence of coordination between MNOs, it is still advantageous for the network to be aware of multi-SIM UEs to avoid degradation of network performance when the UE is switching communication to another MNO after communicating with the current MNO. As mentioned before, network operation is based on timers and algorithms that rely on knowledge of the UE's state to operate efficiently. When the network is not aware of what the UE is doing, these timers and algorithms do not work as intended and degrade network performance. It is therefore equally important for a multi-SIM UE to inform the network of its capabilities when it registers with the network and when it becomes temporarily unavailable, for example when the UE decides to switch its connection to another MNO. Temporarily unavailable in this context refers to the fact that the UE is planning to switch to another MNO and will not be able to monitor paging opportunities. Thus, the UE is temporarily unavailable until it returns to the current MNO. The following solutions address scenarios where there is no MNO coordination and focus on how the UE can help minimize the occurrence of paging collisions. Note that certain aspects of the solution may be applicable to the single MNO case where both SIMs belong to the same MNO, while other aspects may be applicable to dual Rx, single Tx capable UEs.

UE Registration and Multi-SIM Support Information
The UE registration procedure to the core network configures certain parameters between the UE and the CN so that the UE can receive services that require registration. There are several variations of the registration procedure, from initial registration, to mobility registration update, periodic registration update, and emergency registration. These procedures provide the CN with information to configure the parameters that both the UE and the CN use to communicate with each other. For example, the DRX parameters help define a discontinuous reception cycle where the UE is on for some period to monitor paging requests and off for some other period to help preserve battery power.

Certain additional parameters are proposed to be added to the registration procedure so that the UE can provide information to the core network to assist in avoiding paging collisions. These new parameters are summarized in the following list, grouped together and may be referred to as Multi-SIM Support Information. Multi-SIM Support Information may be provided to the core network during the registration procedure to enable it to better handle multi-SIM traffic by adjusting the paging strategy to minimize waste of network and paging resources, especially when the UE is in registration suspended state.
Paging Criteria: Criteria that specify certain conditions that the network uses to page the UE if a condition or event is met for paging. The UE can derive the paging criteria based on the user configuration found in the service prioritization list, and the paging criteria can consist of a list of service type categories and priority levels. The UE provides this parameter to the network of criteria to use when attempting to page the UE. This criteria can be provided by the UE to trigger the CN to filter the transmission of certain pages during times when the UE may not be actively monitoring the PO because it is attached to another MNO to serve another SIM. For example, the service categories mentioned above can be used for the paging criteria that the UE configures the network to filter which paging requests to send. If additional information such as the user phone number, PDU Session ID, and Application ID are provided, the filters can be more granular. Examples can include, for example, calls with the associated phone number, text messages associated with the user, or other data (e.g. Internet data) traffic associated with the PDU Session ID or Application ID. Alternatively, the additional information can provide different priority levels for each service type. The criteria may be a whitelist containing different combinations of service categories, e.g., calls from family, texts from family and best friends, and other data (e.g., Internet data) from a particular PDU Session ID. Based on these criteria, the core network pages the UE only when the downlink data meets one or more of these criteria, thereby saving paging resources for data of no interest to the user. In addition, paging criteria may include criteria such as time period, location information, and UE state when paging request filtering is applicable.
Restricted Paging Area: The UE can request that the CN restrict the paging areas to which it sends paging messages if the UE is attached to another MNO and cannot respond to the page. The parameter can specify that the network should only page the UE in the last tracking or registration area in which the UE was. The parameter can even specify the number of times the network should attempt to page the UE before stopping the page. This can help reduce the waste of paging resources in the network's cells that are outside the UE's current tracking or registration area. When the CN receives a mobile registration update containing this indication, it can check the UE's tracking and registration areas, which it can provide to indicate that the UE may switch its connection to another MNO.
Paging Occasion Separation: The UE can provide this parameter to configure the desired PO separation when the UE requests a new temporary identifier (and associated PO) based on the detection of a potential paging collision. The UE can provide this parameter to request the network to provide a new temporary identifier whose associated PO is a certain distance in time, e.g., an interval based on the number of paging frames, slots, etc. from the currently assigned PO, or the parameter can represent a descriptive enumeration such as "far away,""closeby," or "different," to give the network flexibility in assigning temporary identifiers. A request for "different" paging occasions can be an indication that the UE desires paging occasions that occur at the same periodicity but at different times. Thus, this can be an indication that a different offset is desired.
Number of missed pages before notification: The value determines the threshold number of times the CN detects that the UE has missed receiving a page before notifying the UE. The UE can configure this value during initial registration, where it also informs the CN that the UE is a multi-SIM device. Alternatively, the value may be operator configured through operator policy or through commands received from the operator's operations and management application.
Multi-SIM indicator: The UE may also provide a multi-SIM indicator similar to the one described above, although in this case the resulting functionality may be different. In this scenario, the multi-SIM indicator may allow the CN to configure one or more of the parameters described above and provision the UE with a new temporary identifier that meets those criteria. If both SIMs belong to the same MNO, the registration request may also include an identifier of the other SIM, e.g., IMSI or 5G-GUTI, to inform the core network that the UE supports multiple SIMs and possibly provide specific network optimizations for multiple SIM registration. With the multi-SIM indicator and the identifier of the other SIM, the core network may be able to assign a temporary identifier for the current SIM, whose paging occasions align with those of the other SIM as described above. Thus, the paging occasions of both SIMs in the UE are aligned and the UE only needs to monitor one paging occasion.
Proposed Temporary Identifier: The UE can propose a temporary identifier using this parameter that it determines will avoid paging collisions with the PO of another SIM. Again, the UE can propose a temporary identifier whose paging occasions align with the paging occasions of the UE's other SIM. Alternatively, the UE may propose a portion of the temporary identifier (e.g., the portion used to calculate the paging occasion) and the network may assign the remainder of the temporary identifier.

The UE may provide these parameters at initial registration to initialize the parameters that the CN uses when generating a particular configuration. Similarly, the UE may also include these parameters, for example, in a mobility registration update or periodic registration update procedure after the UE has determined that a potential paging collision exists between the POs of the two SIMs and is requesting a new temporary identifier (and associated PO) from the CN. Although the description shows the UE providing the proposed parameters to the CN, it is understood that the parameters may be configured by the CN, for example as a partial operator policy. Figure 34 shows a UE requesting a new temporary identifier and associated PO from the CN using a mobility registration update procedure. Note that the terms PLMN1 and PLMN2 are used to represent MNOs that are not aligned to be consistent with other figures of this disclosure.

Step S3402: A multi-SIM UE first registers with PLMN1 and receives a temporary identifier for SIM1. The UE then registers with PLMN2, possibly after disconnecting from PLMN1. The UE receives a temporary identifier for SIM2.
Step S3404: The UE uses the temporary identifier to calculate the paging occasions associated with each SIM. Based on the timing information the UE has for each PLMN, the UE detects that there may be a paging collision, as shown in Figure 35. Although the timing relationship between the PLMNs is asynchronous, the UE may be able to detect a paging collision by overlapping two timing references together to obtain a single timing reference. Figure 35 shows that the paging frames associated with each PLMN and these paging occasions overlap even if the superframe timing is not aligned. Note that the POs do not necessarily have to overlap to cause a paging collision. If the POs are close enough to each other, the UE may not have enough time to switch the connection from one PLMN to another, which may also cause a paging collision. Each time the UE needs to perform this operation, there is a certain latency associated with the procedure, e.g., the UE has to tune the radio to the appropriate frequency, perform cell search, PLMN selection, etc.
Step S3406: When the UE detects that there is a possibility of a paging collision, then the UE can request from one of the PLMNs another temporary identifier that generates a paging occasion different from the current one. The UE sends a mobility registration update and can include the proposed parameters listed above, such as PO separation. The UE can also configure the PLMN to page the UE only for certain data, such as voice calls and SMS messages, using the paging criteria parameter. In addition, the UE can configure the CN to restrict the paging area to the last tracking or registration area where the UE contacted the CN, in order to minimize the waste of paging resources in other tracking or registration areas. The UE may also include only the multi-SIM indicator to have the CN provide a new temporary identifier corresponding to another PO or propose a new temporary identifier whose PO location is different from the current PO. The UE may have discovered that the CN supports multi-SIM functionality because the CN has been pre-provisioned with the information, or it may have received the information in a previous registration accept message, such as information provided in a multi-SIM policy, or by reading system information.
Step S3408: The AMF returns a registration accept message, which may include a new temporary identifier. The new temporary identifier may correspond to another PO at a different location than the previous PO. The UE checks the timing of the new PO with the PO of another SIM to ensure that there is no possibility of paging collision. If the UE still detects a paging collision, the UE may repeat step S3406 to obtain another temporary identifier. This time, the UE may use different values of the previously transmitted parameters to try to obtain a temporary identifier with a different PO that does not cause a paging collision. Alternatively, the UE may propose a temporary identifier that it determines avoids paging collisions with POs of other PLMNs.

The paging criteria may be provided by the UE in one of the registration procedures to configure the CN to filter when to page the UE when the UE activates the registration pause timer, which will be described in more detail later. The criteria may be sent during initial registration to statically configure the CN, or during mobility or periodic registration update procedures to dynamically configure the CN of the UE's preferences in CN filtering paging requests. Alternatively, the criteria may be provided in a service request when the UE wants to inform the network that it is busy and stop paging the UE for a certain period of time. The criteria may be, for example, a white or black list of service categories/prioritization that the UE wants the CN to filter when deciding to page the UE. The criteria may also include more granular information included in the paging message, such as, for example, telephone number, PDU session ID, and application ID.

Paging criteria can be used in UEs with dual Rx, single Tx capabilities to allow the CN to page the UE for important data that the user may want to be paged for. This can reduce the overhead imposed on the UE to respond to pages that the UE may not be interested in. For example, in a business/personal subscription use case, a user may only want to receive calls from his/her boss and fellow team members during the weekend, and no one else. Paging criteria can be set before the start of the weekend to only allow calls from those people. Conversely, a user may want to preempt incoming pages and set paging criteria to not page the UE for all traffic.

(Request for Multiple Paging Occasions)
Since the timing relationship between cells of different MNOs is asynchronous and may vary from cell to cell, having a single PO may cause paging collisions in some cells but not in others. In these cases, it may be better to provision the UE with multiple POs and allow the UE to listen to a PO that does not collide with another SIM's PO. In this case, the UE may dynamically decide which of the multiple POs to listen to for paging requests based on its internal timing per MNO. This option may be used if the single PO case still results in paging collisions.

To request multiple paging occasions, the UE can include a multi-PO indication in one of the registration requests, such as a mobility registration update or periodic registration update procedure. The indication can specify the number of desired temporary identifiers to be assigned to the UE, or simply a flag that the UE requests multiple temporary identifiers, causing the core network to provision many temporary identifiers for the UE. The UE can combine any of the other parameters described herein to assist the core network in allocating temporary identifiers corresponding to the desired PO characteristics. For example, a paging occasion separation parameter can be used to indicate the desired separation between multiple POs.

When the UE receives a temporary identifier associated with a PO, the UE decides which PO to monitor based on the POs it has for other SIMs. Thus, if the UE moves between cells and the PO of any SIM shifts, the UE can dynamically decide which of multiple POs to monitor to avoid paging collisions. When the UE responds to the page, the network can stop paging the UE on the other POs assigned to the UE. The UE may request multiple temporary identifiers from each MNO to give it maximum flexibility to avoid paging collisions. For example, the UE may request two temporary identifiers each from MNO1 and MNO2, requesting the desired PO separation that allows the UE to avoid paging collisions between the four assigned POs, regardless of mobility.

The restricted paging area parameter may be used with a request for multiple paging occasions to offset the paging resource overhead introduced by having multiple paging occasions. As previously mentioned, the restricted paging area parameter may specify that the area in which the CN pages the UE is to be restricted to the UE's last known tracking or registration area. This parameter may be used to limit paging escalation that may occur when the CN expands the area in which it pages the UE if the UE does not respond to a page. Since the UE has already requested multiple POs, adding the restricted paging area parameter may localize the paging overhead to the tracking or registration area in which the UE last communicated with the CN, thereby saving paging resources in other tracking and registration areas.

(Simultaneous pages on the same paging occasion)
If the SIMs belong to the same MNO and the CN has assigned temporary identifiers to the SIMs to correspond to the same PO, there may be cases where data is available simultaneously for both SIMs and the CN then pages the UE. During these cases, the paging record of the paging message contains a UE identifier that matches that of the temporary identifiers of each of the SIMs. This problem arises as to which SIM's UE completes the processing of the paging request.

This problem can be easily addressed by allowing the UE responding to the paging request to include in the service request sent to the CN a list of PDU session IDs corresponding to both SIMs. To do this, it is proposed that a new parameter is included in the service request, including the identifier of the other SIM as well as a list parameter of another activated PDU session. The new parameter may be added to the existing parameter list of the service request procedure so as not to interfere with existing operations. Thus, the service request provides information about one SIM using the existing parameters and about the second SIM with the new parameters. The inclusion of multiple instances of this new parameter can be used to extend support to multiple SIMs, where multiple refers to more than two SIMs. The advantage of adding the new parameter to the service request procedure is that it saves paging resources, and the service request informs the CN to stop paging the UE for data associated with two or more SIMs.

For a more integrated solution, the temporary identifier and the list of PDU sessions to be activated may be combined together and the list of combinations may be specified in the service request procedure. In this case, the new parameter can be considered as a list of key-value pairs, where the key part contains the temporary identifier associated with the SIM and the value part contains the list of PDU sessions to be activated. This solution is more scalable, since the list can be expanded to include as many SIMs as the UE supports, without changing the structure of the message format.

(Registration Pause Timer)
The operation of a multi-SIM UE can be programmed such that the UE periodically switches the connection between PLMNs to serve each SIM installed in the UE. Using this mode of operation as an example, it is proposed that the core network supports a mechanism where the UE can request the suspension of the registration timer maintained by the CN for the UE's registration state. Instead of introducing a new registration state as described above, a new registration pause timer may be introduced. The operation of the registration pause timer may be mutually exclusive with the operation of the current registration timer. For example, when the UE requests activation of the registration pause timer, the registration timer maintained by the CN is paused. This may occur when the UE performs a mobility registration update or a periodic registration update and includes a registration pause indicator to activate the pause timer. Alternatively, the timer can have a dual mode of operation with an indicator to indicate which mode is currently in operation.

The UE may provide a value to use for the registration pause timer to reflect the periodic periods during which the UE is expected to attach to another PLMN. This value may be included in a mobility registration update or periodic registration update to cause the CN to pause the registration timer. Upon receiving this value, the CN may pause the registration timer and activate the registration pause timer. Then, some time later, the UE may revert and deactivate the registration pause timer, re-enabling the registration timer. Figure 36 shows an example of this procedure for activating and deactivating the registration pause timer.

Step S3602: A multi-SIM UE is registered in both PLMN1 and PLMN2. Currently, the UE is in active communication with PLMN1.
Step S3604: The UE's operation programming logic decides to switch the connection from PLMN1 to PLMN2. The UE sends either a mobility registration update or a periodic registration update request to the AMF of PLMN1. The request may include an instruction to activate the registration pause timer or may include an expiration date of the registration pause timer. The value of the expiration date may be configured within the UE's operation parameters, a policy maintained by the UE or configured by the core network, or some other operation metric programmed by the user through a GUI. The UE may also provide an instruction to request the CN to queue any downlink data for the UE while the registration pause timer is running.
Step S3606: Upon receiving the request, the AMF of PLMN1 may pause the registration timer and activate the registration pause timer. The AMF may configure the expiration of the registration pause timer using a value provided by the UE if the registration pause timer was provided. Alternatively, the AMF may use a value configured by the operator of the core network. The AMF still maintains all existing contexts of the UE, including the UE's registration state, security context, and maintenance of existing PDU sessions. However, due to the activation of the registration pause timer, the CN will not page the UE for downlink data until the UE deactivates the registration pause timer. If the UE requests the CN to queue up downlink data while the registration pause timer is running and the CN is able to do so, the CN may enable such functionality by having the AMF provide this indication to the SMF in step S3606a to update any existing PDU sessions of the UE. The SMF then informs the UPF to buffer any downlink data destined for the UE, not shown in the figure. If the policy control request trigger is met, the SMF informs the PCF of the met condition, as shown in step S3606b. The condition may be that the AF subscribes to be notified every time the UE's registration status is suspended. This notification may cause the AF to notify the UE of any data until the suspension is deactivated.
Step S3608: The AMF returns a registration accept message to the UE indicating the status of the request. If the request is granted and if the AMF has changed the registration pause timer expiry value, the AMF includes the new value in the accept response. The AMF can also provide an indication of whether the UE's request for the CN to queue up downlink data was granted when the registration pause timer is running. The UE starts a timer incorporating the value returned by the AMF or the value originally provided to track the remaining time the UE has before the CN initiates the deregistration procedure. In other words, the UE needs to deactivate the registration pause timer maintained in the CN before the UE retention timer expires so that the UE's registration state remains RM-REGISTERED. When the registration pause timer is active, the UE's registration state is RM-REGISTERED and its connection state is CM-IDLE. However, the CN does not page the UE during this time.
Step S3610: The UE disconnects from PLMN1 and connects to PLMN2. Upon connecting to PLMN2, the UE may perform either a mobility registration update or a periodic registration update to deactivate the registration pause timer maintained by the AMF of PLMN2. In the request, the UE may include an instruction to deactivate the registration pause timer or to set the expiration value to zero. The AMF of PLMN2 then disables the registration pause timer and re-enables the registration timer. The expiration of the registration timer may be reset at this point instead of continuing from the previous value when it was paused. If the UE had previously requested the CN to queue up downlink data, the UE will receive those data when the service request is performed. The UE may maintain the connection with PLMN2 as long as the user requires it to use the services associated with SIM2. If the UE is in CM-IDLE state upon expiration of the operation timer, the UE may decide to disconnect from PLMN2 and reconnect to PLMN1.
Step S3612: If the UE decides to reattach to PLMN1, the UE deactivates the registration pause timer and sends either a mobility registration update or a periodic registration update request to PLMN1 to re-enable the registration timer. The UE may provide an indication of the registration pause timer expiry or a zero value to trigger the deactivation of the registration pause timer.
Step S3614: The AMF of PLMN1 deactivates the registration pause timer and re-enables the registration timer. The registration timer expiry may be reset at this point instead of continuing from its previous value when it was paused in step S3606.
Step S3616: Similar to step S3608, the AMF of PLMN1 returns a registration accept response with the status of the update request. If the request of step S3612 was a service request, the UE can start receiving the queued downlink data. If not, the UE can perform a service request after this step to receive the queued downlink data.
Step S3618: It may be the case that the UE is busy processing data associated with a PDU session or is in a call where the UE remains connected to PLMN 2. During these cases, the UE may remain in step S3610 for a time longer than the expiry of the registration pause timer and the deregistration timer. In these cases, the AMF in PLMN 1 may deregister the UE for SIM 1.

As part of the procedure of pausing the registration timer, the CN may also suspend paging of the UE and buffer mobile terminated data for the UE. During this suspension period, the CN recognizes that the UE is not actively listening for paging requests, and as a result, the AMF may instruct the SMF to queue up paging requests and instruct the UPF to buffer the mobile terminated data for the UE, as shown in step S3606a of Figure 36. All security contexts established for NAS signaling and PDU sessions in the user plane are preserved as if the UE was in CM-IDLE state. In fact, during the suspension, the CN and the UE maintain the RM-REGISTERED and CM-IDLE states for the UE. This suspension state is similar to the RRC_INACTIVE state, but applies to the registration and connection management states of the UE. Thus, the UE and the CN can quickly re-establish communication after the UE switches to using the SIM associated with the registration. This behavior can be triggered by including the paging criteria parameters described above when the UE requests activation of the registration pause timer.

UE Request to Stop Paging
In some cases, the UE may be busy using a service in one SIM and then receive a page for another SIM. The paging message may indicate what type of service caused the page. Rather than having the network in the second SIM continue paging the UE, the UE may respond to the page with a service request message to inform the network that the UE is busy and to stop paging the UE. The service request message may include, for example, an indication of which service the UE is currently performing on the other system (e.g., emergency service), which service the UE is responding to on this current system, which service the UE is not responding to on the current system, and a timer value to indicate to the network when the network should attempt to page the UE again for the same type of service. Similarly, when the UE receives a NAS notification containing an indication that the UE should respond to pages and paging causes, the UE can respond with a NAS notification response containing an indication of which services the UE is currently running on the other system (e.g. emergency services), which services the UE is trying to respond to on this current system, which services the UE is not trying to respond to on the current system, and a timer value to indicate to the network when the network will attempt to send a page or NAS notification to the UE again for the same type of service. By the UE informing the network, paging resources can be saved and the network can signal to data sources that the UE is busy, e.g. a voice call goes directly to voicemail instead of trying to page the UE. In an IoT use case, the information provided to the CN can be used to update the UE's reachability status on application servers that are trying to reach the UE.

This feature may be useful when the UE has dual Rx and single Tx capabilities. As shown in Figure 37, the UE is on a call on SIM1 and can receive a page on SIM2. The UE can send a request to the network on SIM2 to inform the network to stop paging the UE. The UE in this case may be actively receiving downlink data on one of the receivers and there may be a gap in the uplink transmission where the UE can send a request message to the network on SIM2. This feature may also be useful when the UE has single Rx and single Tx capabilities, as well as time multiplexing between two SIMs on the same PLMN or between PLMNs of two SIMs. Note that the UE can communicate with the same or different MNOs and the procedure will be the same.

Step S3702: A multi-SIM UE is registered in both PLMN1 and PLMN2. The UE may have dual Rx, single Tx capability, or single Rx, single Tx capability and time multiplexing between the PLMNs of each SIM. In this case, the UE has dual Rx and single Tx capability.
Step S3704: The UE currently receives downlink data on Rx1 and monitors paging on Rx2.
Step S3706: PLMN2 receives data for SIM2 and pages the UE. The page may include service prioritization information indicating what the page is for.
Step S3708: The UE makes a decision to inform PLMN2 that the UE is busy receiving data from PLMN1. To make this decision, the UE can check the service type found in the paging message in a user-configured service prioritization list. For example, the UE may be in the middle of an important voice call and the service type of the paging message indicates an incoming text message. The user can configure the service prioritization list to indicate that the text message has low priority. Alternatively, the UE may have presented the user with a GUI indicating that an incoming text message is pending for SIM2 and that the user has chosen to temporarily ignore the text message. Because the UE is receiving data on Rx1, there may be gaps in time during which the UE is not transmitting any UL data on the single Tx. During these gaps, the UE may be connected to PLMN2, so the UE can perform a request to inform the AMF of PLMN2 to stop paging the UE.
Step S3710: Upon successful connection to PLMN2, the UE may send a mobility registration update request to the AMF of PLMN2. The request may include an instruction to activate the registration pause timer or may include an expiration date of the registration pause timer to indicate that the UE has the AMF temporarily pause paging of the UE for a specified period of time. Alternatively, the instruction may be provided in a service request message with the time when the CN should stop paging the UE and the updated multi-SIM support information. The UE may also provide an instruction to have the CN queue any downlink data for the UE while the registration pause timer is active. The UE may then retrieve the queued downlink data after the UE re-establishes communication with the CN.
Step S3712: The AMF of PLMN2 returns the status of the request in an acceptance response. As part of the response, the CN may provide a new value for the expiry of the registration pause timer, as well as whether the CN may queue any downlink data while the registration pause timer is running. The response may include the status of the request and the time at which the CN should stop paging the UE.

Although the above procedure shows the UE registering with two PLMNs (or MNOs), it can also be applied to a scenario where the UE's SIMs all belong to the same MNO. This procedure works in a similar way, except that instead of sending a mobility registration update request or service request to another PLMN, the UE simply sends the request to a single PLMN.

When the UE sends a request to the PLMN to stop paging the UE, the UE may include multi-SIM support information in the request to inform the PLMN when to stop paging the UE, the service types for which the UE will be paged, the service types for which the UE will not be paged, and whether to buffer the UE's data. These pieces of information may be grouped together as additional information that the UE provides to the PLMN to enable the PLMN to filter pages for the UE when the UE is busy. The multi-SIM support information may be organized as a policy that the UE provides to the PLMN or as a set of instructions sent to the PLMN in the service request or during a registration update request.

(The core network provides notification of missed pages to the UE)
Whenever the core network pages a UE and the UE does not respond, the core network can keep track of the time the UE missed the page and notify the UE when the UE next connects to the CN or through another access, e.g., a non-3GPP access. This feature can be enabled if the UE informs the CN that it is a multi-SIM UE during one of the registration procedures or if the UE enables one of the parameters described herein related to multi-SIM operation, such as Multi-SIM Support Information. The CN can inform the UE in response to either the Registration Request or Service Request procedure. The CN can also provide the time the page was sent and the registration and/or tracking area when the UE did not respond to the page. Alternatively, if the UE supports connectivity to multiple access technologies, e.g., via 3GPP access and via non-3GPP access, the CN can send the notification to the UE via an access where the UE may be in CM-CONNECTED state. This information may enable the UE to identify paging collisions and/or problems with the paging process and may enable the UE to utilize one of the solutions mentioned above to help rectify the problem. Note that the following procedure may apply if the SIMs belong to the same MNO and if the UE has dual Rx, single Tx, or single Rx, single Tx capabilities. See Figure 38.

Step S3802: A multi-SIM UE is registered in both PLMN1 and PLMN2. If the two SIMs belong to the same MNO, the UE registers both SIMs in the same PLMN.
Step S3804: The UE is currently receiving downlink data from PLMN1.
Step S3806: PLMN2 receives data for SIM2 and pages the UE. However, the UE does not receive or respond to the page because it received data from PLMN1, e.g., the user is on an important voice call and does not want to be interrupted. The user may have received a prompt from the UE via the GUI but has decided to ignore the prompt. It should be noted that the UE may operate in either single Rx, single Tx, or dual Rx, single Tx capabilities.
Step S3808: After some time, the UE connects to PLMN2.
Step S3810: The UE may perform either a registration procedure or a service request procedure to start receiving services from PLMN2.
Step S3812: In the acceptance response, the AMF of PLMN2 may provide the UE with information of any missed pages that it has stored. The information may include the time of the missed page, the tracking and/or registration area where the page was sent, and possibly additional information about the page, such as the service category, as well as other more detailed information, such as the caller's phone number or text message sender, PDU session ID, and/or application ID. Alternatively, when the UE can connect to multiple access networks, such as 3GPP access and non-3GPP access, the CN may send a notification to the UE via the access network that the UE may be in CM-CONNECTED state. Upon receiving this information, the UE may determine that a paging collision has occurred and identify steps the UE may take to avoid such collisions in the future. The UE may then perform one of the procedures described above to request a new temporary identifier whose PO is separated from the current PO.

Another aspect of this solution is that the CN can wait for a configured number of missed pages before notifying the UE of the missed pages. The number of missed pages may be configured by operator policy, via a command from the operator's operation and management system, or may be provided by the UE as multi-SIM support information. The UE can provide in the multi-SIM support information a threshold number of missed pages that the CN uses to send information to the UE about missed pages during one of the registration procedures indicating to the CN that the UE is a multi-SIM device. The CN then starts tracking the number of times the UE does not respond to a page, and when the threshold is reached, the CN notifies the UE. In the notification, the CN can provide a list of all the times the UE missed an incoming page, including a timestamp, the tracking or registration area where each page was sent, and the number of times the CN tried to page the UE. The CN can also include additional information of what the page was for, such as the service category and prioritization level, such as the phone number, PDU session ID, application ID, etc.

(Graphical User Interface)
FIG. 17 illustrates one exemplary graphical user interface (GUI) that the UE may display to indicate the UE's multi-SIM configuration. The GUI may display a list of multi-SIM policies showing all PLMNs in which the UE is registered and provide the user with a mechanism to configure the priority associated with each registration. For each SIM entry displayed, an active status is shown along with a switch button to allow the user to manually initiate a SIM switching procedure by pressing the button of the associated SIM entry. The GUI may also allow the user access to the information found in Table 4 for the corresponding PLMN by long pressing the associated entry. FIG. 18 illustrates one exemplary GUI of individual SIM configuration information associated with a PLMN registration. The user may further configure specific parameters of a particular PLMN through this GUI.

Figure 33 shows another example GUI for a multi-SIM UE where the UE supports three SIMs. The GUI lists the type of services for which each SIM is enabled. For SIM1, voice, SMS message, and data services are enabled and may represent the primary SIM. SIM2 is enabled for data services only while SIM3 is enabled for both voice and SMS message services. Both SIM2 and SIM3 may be secondary SIMs that may be used while mobile.

An exemplary embodiment of an electronic device is a UE, such as a smartphone. In one exemplary embodiment, the circuitry of the electronic device (e.g., UE) can include at least one or more processor devices (e.g., CPUs). In one exemplary embodiment, the circuitry can also include one or more memories that store computer-executable instructions. In one exemplary embodiment, the circuitry can include one or more of the components shown in FIG. 1F.

In one exemplary embodiment, an electronic device (e.g., a UE) receives data from a core network.

Each feature of this disclosure is defined by the following numbered paragraphs.

Paragraph 1. An electronic device, comprising:
a receiver configured to receive a first subscriber identity module (SIM);
a receiver configured to receive a second SIM; and a circuit,
receiving data from the first SIM;
1. An electronic device comprising: circuitry configured to send a request to a first public land mobile network (PLMN) to register the electronic device with the first PLMN, the request indicating that the electronic device is a multi-SIM device, the request including multi-SIM support information, and the multi-SIM support information informing the first PLMN of a preference of the electronic device for multi-SIM operation.

Paragraph 2. The electronic device of paragraph 1, wherein the multi-SIM support information includes one or more of paging criteria, paging opportunity separation, proposed temporary identifier, restricted paging area, and number of pages missed before notification.

Paragraph 3. The electronic device of paragraph 2, wherein the paging criteria includes at least one of service type category information or service prioritization level.

Paragraph 4. The electronic device of paragraph 3, wherein the service type category information includes one or more of a voice call, an SMS message, other data, control plane signaling, an emergency message, an emergency callback, or mobile terminated exception data.

Paragraph 5. The electronic device of paragraph 4, wherein the other data includes Internet data, application data, or data associated with a protocol data unit (PDU) session.

Paragraph 6. The electronic device of paragraph 3, wherein the service prioritization levels include a numerical level, a high or low level, a level associated with an emergency, or a single level.

Paragraph 7. An electronic device as described in paragraph 2, wherein separation of paging opportunities, suggested temporary identifiers, restricted paging areas, or number of pages missed before notification enhance the network's paging mechanism for multi-SIM operation.

Paragraph 8. An electronic device as described in paragraph 2, in which a user of the device configures preferences for how the device operates for multi-SIM operation.

Paragraph 9. An electronic device as described in paragraph 1, wherein the request is transmitted via a control plane or a user plane.

Paragraph 10. The electronic device of paragraph 1, wherein the electronic device is a user equipment (UE).

Paragraph 11. The electronic device of paragraph 1, wherein the electronic device is configured to send a second request to a second PLMN, the second request including an identifier of a second SIM to be associated with the second PLMN, the first PLMN forwarding the second request to the second PLMN, and the second PLMN authenticating the credentials of the second SIM.

Paragraph 12. The electronic device of paragraph 11, wherein the electronic device includes in the second request a time period, a PDU session identifier, location information, an instruction to buffer the downlink data, and an indication that the electronic device is reachable via the user plane.

Paragraph 13. The electronic device of paragraph 11, wherein the circuitry is configured to receive a temporary ID for use in a paging request from the second PLMN.

Paragraph 14. The electronic device of paragraph 13, wherein the circuitry is configured to update a registration status of the electronic device with the second PLMN.

Paragraph 15. The electronic device of paragraph 13, wherein the second PLMN also updates the registration status of the electronic device with the second PLMN.

Paragraph 16. The electronic device of paragraph 11, wherein the identifier of the second SIM includes SUPI, IMSI, GUTI, 5G-S-TMSI, or SUCI.

Paragraph 17. The electronic device of paragraph 13, wherein while the electronic device is actively registered with the first PLMN, a temporary ID for the electronic device is used to page the electronic device whenever there is a page for the second SIM.

Paragraph 18. The electronic device of paragraph 1, wherein the request is an initial registration request, a partial registration request, an indirect registration request, a registration update request, an initial attach request, a partial attach request, an indirect attach request, or a tracking area update (TAU) request.

Paragraph 19. A method performed by an electronic device, the method comprising:
1. A method comprising: receiving data from a first subscriber identity module (SIM); and sending a request to a first public land mobile network (PLMN) to register an electronic device with the first PLMN, the request indicating that the electronic device is a multi-SIM device, the request including multi-SIM support information, and the multi-SIM support information informing the first PLMN of a preference of the device for multi-SIM operation.

Paragraph 20. When executed by an electronic device, the electronic device:
1. A non-transitory computer-readable medium comprising computer-executable instructions for: receiving data from a first subscriber identity module (SIM); and sending a request to a first public land mobile network (PLMN) to register an electronic device with the first PLMN, the request indicating that the electronic device is a multi-SIM device, the request including multi-SIM support information, and the multi-SIM support information informing the first PLMN of a preference of the device for multi-SIM operation.

Paragraph 21. An electronic device, comprising:
a receiver configured to receive a first subscriber identity module (SIM);
a receiver configured to receive a second SIM;
a circuit configured to receive data from the first SIM;
a first public land mobile network (PLMN) receives data associated with the temporary ID associated with the first SIM; and the first PLMN forwards a paging request or NAS notification to the second PLMN, the paging request or NAS notification including the temporary ID associated with the first SIM; and the circuitry is configured to receive a paging request or NAS notification from the second PLMN, the paging request or NAS notification being sent to the electronic device on the second PLMN.

Paragraph 22. The electronic device of paragraph 21, wherein the electronic device registers simultaneously with the first PLMN and the second PLMN.

Paragraph 23. The electronic device of paragraph 21, wherein the electronic device has an inactive registration with the first PLMN.

Paragraph 24. The electronic device of paragraph 21, wherein the electronic device has an active registration with the second PLMN.

Paragraph 25. A method performed by an electronic device, the method comprising:
receiving data from a first subscriber identity module (SIM);
a first public land mobile network (PLMN) receiving data associated with a temporary ID associated with the first SIM; and the first PLMN forwarding a paging request or NAS notification to a second PLMN, the paging request or NAS notification including the temporary ID associated with the first SIM; and receiving a paging request or NAS notification from the second PLMN, the paging request or NAS notification being sent to the electronic device on the second PLMN.

Paragraph 26. A non-transitory computer-readable medium containing computer-executable instructions that, when executed by an electronic device, cause the electronic device to receive data from a first subscriber identity module (SIM);
A non-transitory computer-readable medium that causes a first public land mobile network (PLMN) to receive data associated with a temporary ID associated with the first SIM; and the first PLMN forwards a paging request or NAS notification to a second PLMN, the paging request or NAS notification including the temporary ID associated with the first SIM; and receives a paging request or NAS notification from the second PLMN, the paging request or NAS notification sent to an electronic device on the second PLMN.

Paragraph 27. An electronic device, comprising:
a receiver configured to receive a first subscriber identity module (SIM);
a receiver configured to receive a second SIM;
1. A circuit comprising:
receiving data paging information associated with a second SIM while connected to a first public land mobile network (PLMN) using the first SIM;
determining to switch to a second PLMN to retrieve data based on the temporary ID and service type prioritization information provided in the paging information;
11. An electronic device comprising: a circuit further configured to: notify a first PLMN to suspend registration of the first SIM; and establish communication with the second PLMN using the second SIM.

Paragraph 28. The electronic device of paragraph 27, wherein the electronic device is configured to check the service type prioritization against an internal policy and determine that the service type of the second PLMN is of higher priority than the service type of the first PLMN.

Paragraph 29. The electronic device of paragraph 27, wherein the electronic device is configured to update the registration status of the first SIM to an inactive registration state, and the first PLMN also updates the registration status of the electronic device of the first SIM.

Paragraph 30. A method performed by an electronic device, the method comprising:
receiving data paging information associated with a second subscriber identity module (SIM) while connected to a first public land mobile network (PLMN) using the first SIM;
determining to switch to a second PLMN for retrieving data based on the temporary ID and service type prioritization information provided in the paging information;
1. A method comprising: notifying a first PLMN to suspend registration of a first SIM; and establishing communication with a second PLMN using a second SIM.

Paragraph 31. A non-transitory computer-readable medium containing computer-executable instructions that, when executed by an electronic device, cause the electronic device to receive paging information for data associated with a second subscriber identity module (SIM) while connected to a first public land mobile network (PLMN) using the first SIM;
determining to switch to a second PLMN to retrieve data based on the temporary ID and service type prioritization information provided in the paging information;
A non-transitory computer-readable medium for informing a first PLMN to suspend registration of a first SIM; and establishing communications with the second PLMN using a second SIM.

Paragraph 32. An electronic device, comprising:
a receiver configured to receive a first subscriber identity module (SIM);
a receiver configured to receive a second SIM; and a circuit comprising:
1. An electronic device comprising: circuitry configured to send a request to a first public land mobile network (PLMN), update a registration timer of the second SIM on the second PLMN, the first PLMN forwarding the request to the second PLMN, the second PLMN updating a registration status of the second SIM in the second PLMN, and the second PLMN returning a response to the first PLMN; and receiving a response, the response being the response forwarded by the first PLMN.

Paragraph 33. The electronic device of paragraph 32, wherein the request is a registration update, a tracking area update, or an inactivity registration timer update.

Paragraph 34. The electronic device of paragraph 32, wherein the request includes a temporary identifier associated with the second SIM.

Paragraph 35. The electronic device of paragraph 33, wherein the second PLMN assigns a new temporary identifier to the second SIM.

Paragraph 36. An electronic device, comprising:
a receiver configured to receive a first subscriber identity module (SIM);
a receiver configured to receive a second SIM; and a circuit comprising:
collecting cell measurements of a second public land mobile network (PLMN) during an attempt to connect from the first PLMN to the second PLMN after deciding to switch to the second PLMN;
1. An electronic device comprising: a circuit configured to store cell measurements of a second PLMN after a connection to the second PLMN fails and receive a cause code; and connect to a first PLMN and provide the collected measurements and cause code of the second PLMN to the first PLMN, the first PLMN forwarding the collected measurements and cause code of the second PLMN to the second PLMN.

Paragraph 37. The electronic device of paragraph 36, wherein if the electronic device successfully connects to the second PLMN, the electronic device formats the cell measurements into a drive test minimization report to a RAN node of the second PLMN.

Paragraph 38. The electronic device of paragraph 36, wherein the stored cell measurements indicate signal strengths of cells belonging to the second PLMN.

Paragraph 39. The electronic device of paragraph 36, wherein the stored cell measurements include the location and time the measurements were taken.

Paragraph 40. The electronic device of paragraph 36, wherein the stored cell measurements may be buffered by the electronic device and transmitted to the RAN node upon a future successful connection.

Paragraph 41. An electronic device, comprising:
a receiver configured to receive a first subscriber identity module (SIM);
a receiver configured to receive a second SIM; and a circuit comprising:
Registering the electronic device with a first public land mobile network (PLMN);
receiving a first temporary identifier from a first PLMN with an associated paging occasion for the first SIM;
registering the electronic device with a second public land mobile network (PLMN);
receiving a second temporary identifier from a second PLMN with an associated paging occasion for the second SIM;
1. An electronic device comprising: a circuit configured to determine a likelihood of a paging collision between a paging occasion of a first SIM and a paging occasion of a second SIM; and to request, from a first PLMN, a new first temporary identifier having a paging occasion different from the paging occasion of the first SIM, or to request, from a second PLMN, a new second temporary identifier having a paging occasion different from the paging occasion of the second SIM.

Paragraph 42. The electronic device of paragraph 41, wherein the request is one of an initial registration, a mobile registration update, a periodic registration update, an attach, or a tracking area update request.

Paragraph 43. The electronic device of paragraph 41, wherein the request includes multi-SIM support information for assisting the first PLMN in allocating a new first temporary identifier or for assisting the second PLMN in allocating a new second temporary identifier.

Paragraph 44. The electronic device of paragraph 43, wherein the parameters include one or more of paging criteria, restricted paging areas, paging opportunity separation, multi-SIM indicator, temporary identifier, and multi-paging opportunity.

Paragraph 45. A method performed by an electronic device, the method comprising:
receiving data from a first subscriber identity module (SIM);
receiving data from a second SIM;
registering an electronic device with a first public land mobile network (PLMN);
receiving a first temporary identifier from a first PLMN with an associated paging occasion for the first SIM;
registering the electronic device with a second public land mobile network (PLMN);
receiving a second temporary identifier from a second PLMN with an associated paging occasion of the second SIM;
determining a likelihood of a paging collision between a paging occasion of a first SIM and a paging occasion of a second SIM; and requesting from a first PLMN to obtain a new first temporary identifier having a paging occasion different from the paging occasion of the first SIM or requesting from a second PLMN to obtain a new second temporary identifier having a paging occasion different from the paging occasion of the second SIM.

Paragraph 46. A non-transitory computer-readable medium containing computer-executable instructions that, when executed by an electronic device, cause the electronic device to:
receiving data from a first subscriber identity module (SIM);
receiving data from the second SIM;
Registering the electronic device with a first public land mobile network (PLMN);
receiving a first temporary identifier from a first PLMN with an associated paging occasion for the first SIM;
registering the electronic device with a second public land mobile network (PLMN);
receiving a second temporary identifier from a second PLMN with an associated paging occasion for the second SIM;
determining a likelihood of a paging collision between a paging occasion of a first SIM and a paging occasion of a second SIM; and requesting to obtain from a first PLMN a new first temporary identifier having a paging occasion different from the paging occasion of the first SIM or requesting to obtain from a second PLMN a new second temporary identifier having a paging occasion different from the paging occasion of the second SIM.

Paragraph 47. An electronic device comprising:
a receiver configured to receive a first subscriber identity module (SIM); and a circuit,
registering the electronic device with a first public land mobile network (PLMN), the first PLMN starting a registration timer;
1. An electronic device comprising: circuitry configured to: send a request to a core network to activate a registration pause timer, the core network pausing the registration timer and starting the registration pause timer; and receive a response from the core network that the registration pause timer is active.

Paragraph 48. The electronic device of paragraph 47, wherein the request is one of an initial registration, a mobile registration update, a periodic registration update, an attach, or a tracking area update request.

Paragraph 49. Providing an expiration value for the registration pause timer;
48. The electronic device of paragraph 47, further configured as follows:

Paragraph 50. Requesting the core network to queue any downlink data for the electronic device while the registration pause timer is running;
48. The electronic device of paragraph 47, further configured as follows:

Paragraph 51. Receiving an indication from a core network, the indication indicating that the core network is to queue downlink data;
51. The electronic device of paragraph 50, further configured as follows:

Paragraph 52. A method performed by an electronic device, the method comprising:
receiving data from a first subscriber identity module (SIM);
registering the electronic device with a first public land mobile network (PLMN), the first PLMN starting a registration timer;
1. A method comprising: sending a request to a core network to activate a registration pause timer, where the core network pauses the registration timer and starts the registration pause timer; and receiving a response from the core network that the registration pause timer is active.

Paragraph 53. A non-transitory computer-readable medium containing computer-executable instructions that, when executed by an electronic device, cause the electronic device to receive data from a first subscriber identity module (SIM);
registering the electronic device with a first public land mobile network (PLMN), the first PLMN starting a registration timer;
1. A non-transitory computer-readable medium for causing a mobile station to: send a request to a core network to activate a registration pause timer, the core network pausing the registration timer, starting the registration pause timer, and receiving a response from the core network that the registration pause timer is active.

Paragraph 54. An electronic device comprising:
a receiver configured to receive a first subscriber identity module (SIM);
a receiver configured to receive a second SIM, the electronic device having a registration of the first SIM and the second SIM; and a circuit,
receiving data of a first SIM;
An electronic device comprising: a circuit configured to receive a page of a second SIM; and to send a notification to a core network about a problem with the paging process.

Paragraph 55. The electronic device of paragraph 54, wherein the notification is a request sent by the electronic device.

Paragraph 56. The electronic device of paragraph 55, wherein the request is one of a mobile registration update, a periodic registration update, a tracking area update, or a service request.

Paragraph 57. The electronic device of Paragraph 54, further configured to: provide an indication to the core network to stop paging the electronic device.

Paragraph 58. A method performed by an electronic device, the method comprising:
receiving data from a first subscriber identity module (SIM), the electronic device having registrations for the first SIM and a second SIM;
receiving a page on a second SIM; and sending a notification to a core network about a problem with the paging process.

Paragraph 59. A non-transitory computer-readable medium containing computer-executable instructions that, when executed by an electronic device, cause the electronic device to receive data from a first subscriber identity module (SIM), the electronic device having registration of the first SIM and the second SIM.
A non-transitory computer-readable medium for causing a second SIM to receive a page; and sending a notification to a core network about a problem with the paging process.

It will be appreciated that any of the methods and processes described herein may be embodied in the form of computer-executable instructions (i.e., program code) stored on a computer-readable storage medium, which when executed by a machine, such as a computer, a server, an M2M terminal device, an M2M gateway device, etc., performs and/or implements the systems, methods, and processes described herein. Specifically, any of the steps, operations, or functions described above may be implemented in the form of such computer-executable instructions. Computer-readable storage media include both volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, although such computer-readable storage media do not include signals. Computer-readable storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disk (DVD) or other optical disk storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or any other physical medium that can be used to store desired information and that can be accessed by a computer.

In describing preferred embodiments of the subject matter of the present disclosure, as illustrated in the figures, specific terminology is employed for the sake of clarity. However, the claimed subject matter is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.

Thus, it will be appreciated by those skilled in the art that the disclosed system and method may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered to be illustrative and not restrictive in all respects. It is not exhaustive and is not intended to limit the disclosure to the precise forms disclosed. Modifications and variations are possible in light of the above teachings or may be obtained from the practice of the present disclosure without departing from the breadth or scope. Thus, although specific configurations have been described herein, other configurations may be employed. Numerous modifications and other embodiments (e.g., combinations, rearrangements, etc.) are enabled by the present disclosure and are within the purview of those skilled in the art and are considered to be within the scope of the disclosed subject matter and any equivalents thereof. Features of the disclosed embodiments may be combined, rearranged, omitted, etc., within the scope of the present invention to produce additional embodiments. Moreover, certain features may be used advantageously without the corresponding use of other features. Accordingly, applicants intend to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of the disclosed subject matter.

Reference to an element in the singular does not mean "one and only one" unless expressly stated, but rather "one or more." Furthermore, when phrases similar to "at least one of A, B, or C" are used in the claims, this phrase is intended to be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or any combination of elements A, B, and C may be present in a single embodiment, e.g., A and B, A and C, B and C, or A, B, and C.

No claim element herein should be construed under the provisions of 35 U.S.C. 112(f) unless the element is expressly recited using the phrase "means for." As used herein, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, and a process, method, article, or apparatus that includes a list of elements may include not only those elements, but other elements not expressly recited or inherent to such process, method, article, or apparatus. The scope of the invention is indicated by the claims that follow, rather than by the foregoing description, and all changes within the meaning and scope of the claims are intended to be embraced therein.

The following [1] to [9] are incorporated herein by reference in their entirety.
[1] 3GPP TS 23.501, System Architecture for 5G Systems, Stage 2, V16.0.0 (2019-03).
[2] 3GPP TS 23.502, 5G System Procedures, Stage 2, V16.0.0 (2019-03).
[3] 3GPP TS 23.503, Policy and Charging Control Framework for 5G Systems, Stage 2, V16.0.0 (2019-03).
[4] 3GPP TS 38.300, General Description of NR and NG-RAN, Stage 2, V15.4.0 (2018-12).
[5] 3GPP TS 38.304, User Equipment (UE) Procedures in Idle Mode and RRC Inactive State, V15.2.0 (2018-12).
[6] 3GPP TR 22.834, Research on Support for Multi-USIM Devices, V0.1.0 (2019-05).
[7] 3GPP S 2-1904722, Introduction of Slice-Specific Authentication and Authorization (TS 23.501).
[8] 3GPP S 2-1904723, Introduction of Slice-Specific Authentication and Authorization (TS 23.502).
[9] 3GPP TS 23.401, General Packet Radio Service (GPRS) Enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Access, V16.3.0 (2019-06).

Claims (21)

1. An electronic device including a first subscriber identity module (SIM ) and a second SIM, the first SIM associated with a first network and the second SIM associated with a second network, the electronic device comprising:
sending a request to the first network to register the electronic device , the request indicating that the electronic device is a multi-SIM device, the request including a subscriber identifier associated with the first network , the request including a multi-SIM policy, the multi-SIM policy informing the first network of a capability of the electronic device for multi-SIM operation ;
determining to switch to the second network;
sending an indication of the decision to switch to the second network to the first network;
An electronic device configured to transition to a CM-IDLE state and an RRC_IDLE state in the first network . The multi-SIM policy includes:
an indication that the electronic device is capable of transmitting service prioritization information that may be used by the first network to determine whether to transmit a paging message to the electronic device;
an indication that the electronic device is capable of receiving service type information in the paging message; or
The electronic device of claim 1 , further comprising one or more indications that the electronic device is capable of providing an identifier that can be used to determine a paging occasion . and receiving information for configuring the electronic device for multi-SIM operation, the information comprising:
an indication that the first network is capable of receiving service prioritization information that may be used by the first network to determine whether to send a paging message to the electronic device;
an indication that the first network may transmit service type information in a paging message to the electronic device; or
The electronic device of claim 1 , further comprising one or more indications that the first network supports transmission of an identifier that can be used to determine paging occasions . 2. The electronic device of claim 1 , configured to send a SIM switching request to the first network, the SIM switching request indicating to the first network that the electronic device will connect to the second network . The electronic device of claim 4 , wherein the SIM switching request includes service prioritization information for requesting that a core network of the first network filter paging requests for the electronic device . The electronic device of claim 1 , configured to receive a paging message from the first network, the paging message including service type information indicating what the paging message is for . The electronic device of claim 6 , wherein the service type information includes one of a voice call, an SMS message, other data, control plane signaling, an emergency message, an emergency callback, or mobile terminated exception data. receiving a paging message from a first network;
The electronic device of claim 1 , wherein the request is sent to the first network in response to receiving the paging message, the request including an indication that the electronic device is busy . 10. The electronic device of claim 8 , wherein the request indicating that the electronic device is busy includes service prioritization information to inform a core network of the first network to filter paging requests for the electronic device . sending a request to the first network to provide a new identifier for calculating a paging occasion;
receiving a response from the first network, the received response including a new identifier;
The electronic device of claim 1 , configured to calculate a paging occasion using the new identifier . The electronic device of claim 10 , wherein the request to the first network to provide a new identifier includes a value used by a network function to determine the new identifier. The electronic device of claim 1 , wherein the electronic device is a user equipment (UE) . 1. A method performed by a network function of a first network, the method comprising:
receiving a request from an electronic device to register the electronic device with the first network, the request indicating that the electronic device is a multi-Subscriber Identity Module (SIM) device, the request including a subscriber identifier associated with the first network, the request including a multi-SIM policy, the multi-SIM policy informing the network function of a capability of the electronic device for multi-SIM operation;
receiving an indication from the electronic device that the electronic device has decided to switch to a second network;
The method includes transitioning the electronic device to a CM-IDLE state and an RRC_IDLE state . The multi-SIM policy includes:
an indication that the electronic device is capable of transmitting service prioritization information that may be used by the first network to determine whether to transmit a paging message to the electronic device;
an indication that the electronic device is capable of receiving service type information in a paging message; or
14. The method of claim 13 , including one or more of the indications that the electronic device is capable of providing an identifier that can be used to determine a paging occasion. transmitting to the electronic device information for configuring the electronic device for multi-SIM operation, the information comprising:
an indication that the first network is capable of receiving service prioritization information that may be used by the first network to determine whether to send a paging message to the electronic device;
an indication that the first network may transmit service type information in a paging message to the electronic device; or
14. The method of claim 13 , further comprising one or more of the indications that the first network may transmit an identifier that may be used to determine a paging occasion. 14. The method of claim 13 , further comprising receiving a SIM switching request, the SIM switching request indicating to a network function that the electronic device connects to a second network . 17. The method of claim 16 , wherein the SIM switching request includes service prioritization information to request that a network filter paging requests for the electronic device. 14. The method of claim 13, further comprising sending, by the network function, a paging message to the electronic device, the paging message including service type information indicating what the paging message is for, the service type information including a voice call, an SMS message, other data, control plane signaling, an emergency message, an emergency callback, or mobile terminated exception data . 14. The method of claim 13, further comprising: sending, by the network function, a paging message to the electronic device; and receiving, by the network function, a response to the paging message, the response including an indication that the electronic device is busy and service prioritization information to request that the network function filter paging requests for the electronic device . The network function
receiving a request from the electronic device to provide to the network function a new identifier for calculating a paging occasion, the request to the network function to provide to the network function a new identifier for calculating a paging occasion including a value that can be used by the network function to determine the new identifier;
14. The method of claim 13, further comprising: sending, by the network function, a response to the electronic device including a new identifier for calculating paging occasions; and using, by the network function, the new identifier for calculating paging occasions. 1. An electronic device including a first subscriber identity module (SIM) and a second SIM, the first SIM associated with a first network and the second SIM associated with a second network, the electronic device comprising:
sending a request to the first network to register the electronic device, the request indicating that the electronic device is a multi-SIM device, the request including a subscriber identifier associated with the first network, the request including a multi-SIM policy, the multi-SIM policy informing the first network of a capability of the electronic device for multi-SIM operation;
sending an indication to the first network that the electronic device is switching to the second network;
An electronic device configured to transition to a CM-IDLE state and an RRC_IDLE state in the first network.

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